Featured Review: Asus Zenfone 2 (ZE551ML)

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At CES in Las Vegas this year Asus announced the Zenfone 2, the followup to the successful line of Zenfone smartphones it produced last year.  The last time we were graced with the opportunity to review an Asus phone was back in October last year, and now it’s time to put Asus newest product to the test.  At CES Asus spoke of offering a phone with specs that match the biggest players on the block but with a price that could cut them at the knees.  They deemed this strategy “luxury for everybody,” and it was an immediate hit thanks to the incredible specs and price points that Asus laid down on the table.  Today we’re reviewing the top-end phone in the line of Zenfone 2’s, the ZE551ML, so let’s take a look at the best that Asus can offer its customers.



Looking below you’d expect a phone carrying such specs to retail for quite a few hundred dollars off contract, and likely around $200 on contract if you’re in the US.  What’s amazing here is that Asus is selling this for less than $350 off contract, with even better deals coming around every so often too.

  • 5.5-inch 1080p IPS Display
  • Intel Atom Z3580 2.3GHZ Quad-Core CPU
  • PowerVR Rogue G6430 GPU
  • 4GB of RAM
  • 16/32/64GB internal storage, microSD card support
  • 3,000mAh Li-Po battery, non-removable
  • Android 5.0 Lollipop, ZenUI Skin
  • 13MP rear-facing camera, Dual-tone dual-LED flash
  • 5MP front-facing camera
  • 152.5mm tall x 77.2mm wide x 10.6mm thick
  • 170g


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1080p displays are nothing new to the world of smartphones, having graced the likes of flagships for over two years now.  We’ve even seen plenty of budget phones use 1080p displays but often times they trade off viewing angles, color accuracy or refresh rate for sheer resolution.  The panel on the Zenfone 2 is certainly a fantastic IPS panel, and likely among the better 1080p IPS panels available on the market.  Viewing angles are generally great, although there is visible black level loss at extreme angles, although colors don’t ever seem to change their hue.  Black levels are deep and representative of a good overall picture, but of course you’ll find deeper blacks on an AMOLED or other higher-quality IPS displays.

The refresh rate is top notch though and I never noticed any ghosting present no matter how contrasting the colors on screen were or how fast they moved.  Outdoor viewing was nothing short of phenomenal and brightness overall was more than adequate.  Overall the panel on the Zenfone 2 is a fantastic one that anyone could be happy with, and any faults would have to be nitpicked to be found.  Asus also used a top-notch digitizer in the Zenfone 2, something that often doesn’t happen at this price point.  This means super fast touch responsiveness, proper multi-touch support without ghost swipes or other calibration issues, and an overall pleasant experience.

Hardware and Build

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Upon first glance the Zenfone 2 looks high-end.  The brushed metal appearance of the back eschews a higher cost product without a doubt, but once you pick up the phone there’s no doubt its made of plastic.  That’s not to say it feels cheap, because it definitely doesn’t, but it doesn’t feel quite as high-end as something like an HTC One, Galaxy S6 or iPhone 6 would, but then again we’re talking phones that literally cost double the price.  One other thing you’ll notice immediately about the design is the complete lack of buttons on the side of the phone.  The volume rocker has been moved to the back, much like LG’s phones, but instead of a power button inbetween the volume buttons as you’d find on LG’s phones Asus has decided to place it on the top of the phone.  This is not a good place for a power button on a phone bigger than 4 inches, and especially not one as big as the Zenfone 2 is.

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Thankfully Asus knows this and offers plenty of ways to turn the phone on and off, which will be discussed later.  The circular camera lens is positioned above the volume rockers with a dual-tone dual-LED flash located above that in perfectly centered fashion.  Three capacitive keys sit below the screen on the face of the phone; a back, home and overview (multi-tasking) key from left to right.  The large 5.5-inch screen is flanked by bezels that aren’t necessarily huge but wouldn’t have been considered small on flagships two years ago.  Below the capacitive keys is a brushed metal chin which both looks attractive and remains small compared to many phones out there.

In general the phone is a joy to hold.  10-plus millimeters is considered thick for any non-ruggedized smartphone nowadays, but Asus has done this because it features an extreme curve on the back.  As has been shown on other phones this curve makes it easier to hold and gives your hand a natural place to rest.  What results is a 5.5-inch phone that feels more like a 5-inch phone in almost every way, much like Motorola has done with the Moto X series.

Performance and Memory


Intel isn’t exactly a well-known name in the mobile space but they’re out to change that in 2015.  Over the years we’ve seen Intel’s products in a number of phones and tablets, but generally speaking Intel has been much better in the desktop segment in terms of both sales and performance-to-battery-usage ratio.  This year they are stepping up their game by not only offering powerful quad-core processors at a great price, but also a 64-bit architecture that can compete with the best from Qualcomm or MediaTek.  In general performance of the phone was blazing fast, with apps taking mere fractions of seconds to appear on screen after being called up.  Running benchmarks puts this one under Snapdragon 800 performance levels in general, but we know that benchmarks aren’t always indicative of real-world performance.  In that arena this is a winner of a chipset, and I never once saw it hiccup or slow down regardless of what was thrown at it.

4GB of RAM is another big selling point for the phone, and that makes it one of the first phones on the market with such a selling point.  Running a 32-bit operating system means that 4GB is essentially the ceiling to how much memory can be addressed, which is part of the reason for moving to 64-bit.  While this isn’t 64-bit Android for one reason or another there’s plenty of great multi-tasking performance to be had here.  Android 5.0 Lollipop’s overview window provides an incredibly fast and intuitive way to multi-task with one hand and switch between apps quickly.  There was never a delay when switching between apps and never a redraw either, which should be expected with this much RAM.  Asus makes it easy to pin apps onto the screen so they can’t be navigated away from, clear all running apps (although you really should never do this), and even provides the designated Google search bar on top so it can always be quickly accessed.

Battery Life


3,000mAh batteries are another industry standard that has been around for quite a while with phones this size.  With that comes the near guarantee that the phone can be used all day without worrying about it dying no matter what you do.  The Zenfone 2 doesn’t deviate from that expectation and in fact does a better job than most at providing great battery life on the go.  In fact Asus went out of their way to help users get the best battery life by including a system app that automatically detects when apps have gone rogue or are unnecessarily draining your battery.  This is a Godsend for many as we’ve seen more then our fair share of individuals who get fed up with their battery draining and not knowing what’s causing the drain.

Standby is as good as I’ve seen on any phone too, with days and days being a very real possibility if you need to keep it on for emergencies when on the go.  Asus has included ultra battery saver mode that’ll only let the phone wake up for specified apps, and a customized mode that lets you dig further into possible battery draining situations like background push messages and data.  There’s even an auto-start manager that allows you to fine-tune apps that automatically start with the phone, giving you deep control over what’s running on your phone.

Phone Calls and Network


Overall call and network quality on the Zenfone 2 was superb.  Calls were as top notch as they could be on a non-HD voice connection, and overall signal strength and quality was solid even in the middle of nowhere.  The version of the Zenfone 2 I had only supported Chinese LTE bands, but Asus is going to be selling enough models of the Zenfone 2 to likely give you LTE coverage no matter where you live.  That means that you’ll get the speed and strength of an LTE signal in areas where supported, and plenty of speed provided by an HSPA signal if you can only get that.  Dual-SIM capability is there for those that need it along with full support for using data, messages or calls on individual networks.  You can even chose to dial or send a message between SIM cards dynamically, which would of course relieve the hassle of having to go back into settings to do such a thing.

Software UI


Like many manufacturers Asus has its own skin of Android, one which it calls ZenUI.  While ZenUI launched on the Android 4.x platform the Zenfone 2 launches with Android 5.0 Lollipop, which featured the largest change over any version of Android to date.  Besides adding tons of features Google completely retooled the look and feel of Android as well as how a number of system-wide settings work.  Asus has largely kept the aesthetic of Lollipop’s design language, Material Design, and has chosen to lighten up the stock color palette a bit over what Google uses.  The result is an ultra-clean and fresh feeling UI, with lots of white everywhere and a splash of color to accent key points.

Starting from the lockscreen you’ll notice that Asus has kept the general look and feel of the Lollipop lockscreen, from its large clock that’s left-justified to the on-screen notifications that can be either swiped away or accessed by double-tapping.  Three quick launch icons are found between the clock and notifications and can be customized to any three apps of your choosing.  Swiping down brings down the full notification shade that gives access to the quick toggles.  Quick toggles are a grid of 16 icons in a 4×4 setup, and can be customized from a large set of choices.  The top row are tools like flashlight, calculator, camera, screenshot, etc., while the remaining 12 icons are for toggles like WiFi, Bluetooth and so on.  This setup is phenomenal as it adds to the Lollipop way of things while not taking away from the beauty aesthetically.

Customization and Features


Asus launcher builds upon what we’ve seen in the past from the company and also uses some trends that have been changing in the industry.  All the bells and whistles from other launchers are here including customized animations, scrolling wallpaper support, etc.  In addition to this Asus has provided a way to easily customize the icons and other assets as well.  This theme support extends to other parts of the system including the notification shade, wallpapers and even the menus and settings.  Asus also provides an easy way to blend wallpapers and the status bar with other colors and images, giving you full control over what your phone’s interface looks like.

Unlike many phones that feel bloated with features the Zenfone 2 feels like it doesn’t go out of its way to overwhelm you or your battery with these features, rather it lets the user explore deeper and deeper into the realm of possibilities that it holds.  Since the power button is up top it’s pretty awkward to press given this is a phone with a 5.5-inch screen.  Thankfully Asus has made a few ways to turn the device on or off without ever having to reach for or press this button.  The famous double-tap-to-wake is here, as well as drawing different letters on the screen while it’s off to launch specific apps.  This list of apps is customizable and can be changed at any time.  Double tapping on the notification bar at any time puts the phone to sleep, as does double tapping on the homescreen when using the Asus launcher.  To make up for not having software keys Asus allows users to customize what the capacitive keys do, and long-pressing and swiping up on the home button brings up Google Now as well.



Most phones come with apps pre-installed and the Zenfone 2 isn’t an exception to that rule.  There’s some bloatware from 3rd parties but it’s not overwhelming nor does it take up much space, however Asus has broken its OS out into separate apps.  This means that Asus can update apps individually without having to issue an entire OS update as has been the case in the past with phones.  This is yet another great trend in the mobile industry that Asus has grabbed and ran with, and a simple “ZenUI Instant Update” option in settings brings you to the Play Store with a listing of all Asus apps.  This is especially great for security patches and bug fixes, not to mention feature additions.  This is for all 30 of Asus’ apps including the camera, calendar, calculator, contacts, file manager, etc.  Including the most basic of system apps is not only smart for Asus, it’s also great for the customer.


Asus suite of software products have improved with every release, and the newest set of ZenUI apps is no exception.  Material design is present in essentially everything on the phone, giving a consistent design and feel to all apps.  The calendar features a new beta mode called What’s Next that provides a consistent notification for your upcoming appointments and other calendar events, something important for many people out there.  Asus even has a support app that covers all of the Asus apps on the phone, gives information about how to use the app and what it does, as well as providing forums for users to ask questions in an easy to remember place.


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Sound output from the Zenfone 2 is nothing short of phenomenal and has certainly provided one of the better audio experiences I’ve seen from a phone.  Everything is here from proper lockscreen music control to a built-in equalizer that’s super easy to use.  Output via Bluetooth or the 3.5mm headset jack was a superb experience that produced excellent audio even without the need for equalization.  Using the built-in equalizer to fine-tune the sound gave me some of the best audio I’ve heard out of a phone, rivaling that of considerably more expensive devices.  The loudspeaker left a little to be desired in the volume department though, and even at the max volume I had a hard time making out what the other person was saying.  This was particularly true on the highway when trying to talk to someone, and I found myself just using the regular earpiece speaker instead for phonecalls.



Asus spent quite a bit of time talking about their new Pixel Master software at CES, and for good reason too.  This new camera software gives users so many options their head may spin, but only once they start digging into what’s available.  At the onset Asus provides a super simple-to-use interface that won’t overwhelm anyone, especially users who are only looking for an easy and basic camera interface.  There’s dedicated shutter and video buttons always present, so a photo or video is only a click away.  The camera can be launched from the lockscreen while the phone is off by double-tapping the volume down button, launching the camera in about 3 seconds from the press.  This is a great way to quickly get to the camera and take that shot which may have otherwise been missed.

Auto mode attempts to detect which of the many shooting modes works best for a given shot.  It won’t switch between shot types automatically but it will provide a visual cue in the form of an icon in the bottom left as to what mode might work best for the current lighting conditions.  HDR and Night mode were normally recommended to me during harsh or dark lighting conditions, although more may be recommended depending on the scenario calculated by the software.  You can see the bevvy of modes available in the screenshots in this section, all of which are similar to modes Samsung has included on its phones since the Galaxy S4.  This means that no matter the situation you can have a mode that’s available to shoot a better photo, but the auto mode works extraordinarily well in most situations as it is.


Low light photography was a strong point of the Zenfone 2, producing images that are both not overly noisy and not overly processed.  Often times manufacturers apply harsh denoise filters and then attempt to sharpen the image afterward, producing a hazy crystal effect on the photo that can often times come out looking like a watercolor painting.  Asus not only doesn’t do this but provides simple tools in the settings menu to adjust almost all steps in the processing algorithm, from sharpening to denoise, saturation, contrast, etc.  It’s absolutely a joy to use this camera and it seems that the more you dig into it the more you’ll get out of it.  HDR could use some work though, as it’s obviously not on-sensor HDR and is processed in software instead.  This leads to abnormally long shutter times between shots, resulting in ghost images even in still environments due to natural hand shake.  There’s also some severe overprocessing that produces unrealistic images with haloing around high contrast points.  This can be fixed in software easily and hopefully will be in a future update to the camera software.

Asus has provided a full manual mode that will make any professional or fledgling camera buff happy.  Every single element of the picture can be adjusted including exposure, ISO and shutter speed via easy to use sliders.  White balance is demonstrated via a colored slider instead of confusing numbers or terms, and manual focus is as easy as it gets on any camera, much less a smartphone camera.  All of these settings take effect on the fly, giving you an instant look at what each setting does and how it’s going to affect the final shot.  This is not only great for beginners who may not know what each setting does, but also great for experts who would rather not wait to see what the shot looks like after taking it.


Overall photos from the Zenfone 2 range from passable to great, but never crossing over the mediocre or excellent lines.  It’s a pretty middle-of-the-road experience where excellent software is obviously held back by a somewhat mediocre sensor, although Asus software team has done a pretty magical job of producing the best this sensor can provide.  I found that it particularly excelled in shots with motion, where the camera would prioritize higher ISO for a quicker shutter.  This is incredibly important on a smartphone camera as these sensors really don’t have a lot of leeway when it comes to lighting conditions, and prioritizing longer shutter speeds means anything moving in the picture could turn out blurry.  If you’ve ever used most of Samsung’s phones you’ll know what I’m talking about here, although Samsung isn’t the only one guilty of this.  Another strong suit here is color accuracy, where the Zenfone 2 nailed the right colors and lighting every single time.

Video quality was passable at best.  It’s better than some phones in this price range but overall pretty disappointing.  Digital image stabilization is only available at 720p, and moving to 1080p doesn’t produce a phenomenal picture by any means.  Everything feels like it’s lower resolution than is actually being shot and the image feels as if it’s been interpolated from that lower resolution to 1080p.  You’re not necessarily going to be mad when you watch video that’s been taken with the Zenfone 2, but it’s likely not going to knock anyone’s socks off either.  Check out the samples below on Flickr for all the full res shots taken with the Zenfone 2!



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Asus has absolutely knocked it out of the park with the Zenfone 2.  With the push to include higher quality components without sacrificing the overall price, Asus has shown it can push the boundaries of what we thought was possible as a given price range.  The processor is fast and never seems to hiccup no matter what’s thrown at it, games run like they were running on a dedicated handheld gaming unit, and multi-tasking performance is perfect thanks to a massive 4GB of RAM included.  Sound output is nothing short of excellent and you’ll be happy no matter what type of sound system you have thanks to the easy to use equalizer built in which provides lots of pre-sets for many scenarios.  The camera consists of an average sensor paired with phenomenal software and produced some overall very impressive photos that were worthy of any phone in this price range.

Asus new software suite provides tons of easy-to-use tools that are well designed both aesthetically and in utility.  Material Design is present in all of Asus apps and gives a consistent look and feel to its apps so as not to keep users guessing where the settings menu or any other important sections might be.  Asus has even broken all of these apps off the main OS, providing timely updates via the Google Play Store (or regional app store) instead of users having to wait for an entire OS update as has been the case in the past.  The phone is not only well designed too but it’s a joy to hold, with a natural curve on the back that makes it feel smaller than most phablets, which is important given its large 5.5-inch screen.  This is certainly one of the best phones launched in this price range ever, and it offers an experience that anyone would be happy with.


In terms of the price, well, that bit is simple. We have a special promotion with our trusted partners Gearbest.com and is the cheapest you will find the Asus ZenFone 2 and thanks to our exclusive deal you can currently pick it up for only $274.99. Click the link below to pick up your ZenFone 2 4GB for only $274.99 but you will need to use the “AndroidHeadlinesZ2DEAL” coupon code to get the special price.This price only applies to the Gray version/ Chinese version.

Asus Zenfone 2 for $274.99