The 6 was a beautiful phone, and IMO their last good phone. It lasted me up until this year, and to be honest, my new Pixel is missing features that I love from OP, like the screen gestures for skipping songs.
I wouldn't trust them with another purchase again, though. I loved the 1 and 6, but never again.
I am on the same boat. Had the op1/2 and have a 6t currently but now my display is broken and the battery is very bad. So I bought a fairphone 5 and am waiting for it's arrival. :)
It's basically an OPPO clone now. Oxygen OS is effectively ColorOS re-marketed. Unless you're chill with Chinese phones and software I would stay far far away.
Even back then OnePlus was sketch as hell. Remember their "ladies, take a pretty selfie and win an OnePlus" campaign?