yep its amazing, using it for 3 days now
(ps: fingerprint will be fixed soon)
I noticed that the camera quality decreases everytime an major update is released, when you compare Nougats Camera and Oreos, it's quite a big...
if he wants to downgrade, then let him do it jeez
Download the full update from downloads.oneplus.com and flash it through recovery. this will wipe internal.
Unofficial Treble is avaible, works great too. just Google it, it's A Type System Treble