So you've flashed the Android N Developer Preview, and you've long pressed the gear icon in the notification shade to open up the System UI Tuner. But now you want to get rid of it. Well, good thing is you don't need to perform a factory reset to do so. There's a pretty simple way to hide it from the settings, actually. And one that is new to Android N, as it's not currently available in Android Marshmallow (to be clear, System UI Tuner is available, but the option to remove it is not).
Simply go into Settings then tap on System UI Tuner. You'll see a overflow menu on the right side, or 3 dots. Tap on that and then you'll see an option to remove. Just tap Remove and you'll be all set. The setting will now be removed from the settings. Just as easy as can be. Now to bring it back, all you need to do is to long-press the gear icon in the notification pull down, until the phone vibrates and System UI Tuner will be available again. It really can't get any easier.
Google has kept the System UI Tuner hidden in Android Marshmallow and Android N, at least for now, simply because these settings are experimental and could have some bugs. Something that most users won't want to deal with. So Google has kept them hidden. However within the System UI Tuner, there are all sorts of options, with the most popular one being the ability to have a night mode on your smartphone. This is especially important for those that are using their phone at night and don't want to get blinded by the searing white color that is used in most of the material design UI these days.
It's important to also remember that this Android N Developer Preview is just that, a developer preview. Some things are broken, actually many things are broken. And there are plenty of bugs. It's definitely worth it to stick to Android 6.0.1 Marshmallow for now, unless you have another smartphone you can use as a daily driver.