I'm currently testing lineageos on a oneplus 6t since it is dirt cheap (from 50€$) ob ebay.
So far my track record has been:
- Around 6 months of daily use
- wifi, bluetooth, lte, gsm all work without issues
- calls work 99% (same as iphone)
- headset needs usbc bc no headphone jack. Works with adapter but so far only for music
- camera works, qr codes work
- nfc works but without google services, ive found no oayment provider thay supports it
- around 16 hrs of battery life under normal use
- no ads in os (or browser, thanks to ublock)
As with all custom roms, you need to unlock the bootloader and if you dont encrypt, you should not do anything on the phone that cant ever be found by a third party, say law enforcement. I would argue that the majority of phones with a locked bootloader arent any better but apparently, if you want that extra security, graphene on a pixel seems to be much more fitting. I have heard of issues with reliability so I'll stick with lineage.
I do develop for and did try postmarketos (actual linux) and I love it. But its absolutely not end user ready from last time i used it. If you tinker and want to help, postmarketos deserves your help but please dont use it as a daily and expect more than 80% reliability. Its for people who love linux and want it to become the real deal and who can manage their frustrations.