I've got a OnePlus 2, it's been an ace phone. It reboots itself every once and a while. But I can't fault the phone. The battery life has been good so far (even with a smart watch connected via Bluetooth). One thing I did have to do is disable the MaxxAudio as it gave me headaches. But I guess that's a personal preference thing. I've had the phone for about 7 months now
You can upgrade the phone to Android 6 (beta firmware) from the following URL:
OnePlus 2 OxygenOS 3.0 Beta | Downloads - OnePlus.net