Battery life has been excellent on the oneplus6. As others have said, there are some major issues, such as GPS and the camera not working at all. Calls were giving me issues a few months ago, but nowadays with “edge” (the latest release) they’re quite reliable.
With all the bugs and problems, I could use PostmarketOS every day with minimal issues, I used it exclusively for just over a week and it was fine. I think in ~2-3 years I’ll be using Linux on mobile as my main device.