Oneplus one was and is the best phone u can get for its price. I myself loved it so much and I bought it in 2014 with an invite. I am using till now and I have got no problems. Its performance feels snappy and camera is great. Only thing I don’t like is its pathetic battery life. As it comes out of the box with custom rom called cyanogenmod which os based on android but brings lots of customisations and cool features. And then its like the nexus range of phones. U will always get an android update but after about 5-6 months of its release. So I am currently on marshmallow with cyanogen os 13.
So I love its os and the way we can customise our phone. Also its the best developer phone out there. So if u do want custom roms other than cyanogenmod u can get it on xda or another sites. Developers like it due to its reliability. When I bought it I was in a doubt because its a chinese company noone has ever heard of. But I can tell u with my experience that I was wrong, I still never had any problems with the phone. Thank you for reading such a long review