OnePlus sells a line of fairly cheap USB Type-C accessories and adapters that seem to work fine with their devices and supposedly can be used on other USB Type-C compliant devices. Google Engineer Benson Leung, however, has a different take on the supplies. According to Leung's research, a certain USB Type-C adapter sold by OnePlus is out of spec and should not be used, particularly with Nexus devices. He says that an incorrect amount of current going into the device can harm it over time. The flaw here is with fast charging, meaning that the OnePlus 2 is in the clear as it doesn't support the technology. Devices with USB Type-C and fast charge should avoid OnePlus' accessories at any cost. Nexus devices come to mind for now, but more are bound to pop up as USB Type-C becomes mainstream over time.
The issue is that most fast charge devices will try to pull down roughly 3 amps of current to charge. The adapter in question, which brings all of OnePlus' USB Type-C accessories under scrutiny, delivers less than that, around the 2.2 amp mark. Still somewhat fast, but when a fast charge device is expecting and is caibrated for 3 amps, only receiving 2.2 can cause undue stress on the battery and the components, with the energy having to go through some of them to get to the battery. Damage over time can be as minor as a loss of battery capacity or could go all the way up to causing a hard brick, where the phone's NAND chip or processor is essentially fried. The extent of possible damage is not known for sure quite yet, since most people don't want to submit their new devices to possible damage.
Various users have contacted OnePlus about this issue. One user received a response stating that this issue has been escalated, while another user spoke with somebody who recommended returning the cables at their own expense for testing. Obviously, this does not bode well for OnePlus' already compromised reputation. In any case, let this post serve as a PSA - do not buy cables and adapters from OnePlus for your fast-charging USB Type-C devices.