Developed by Team POSP, it appears that this port of the update is fully functional and also reported to be stable. However it has been marked as a beta release which means that while it might be stable, there could be some issues or bugs that have yet to be discovered or ironed out, so using it as a daily driver might not be the best idea.
It also does seem to be missing certain features like NFC and VoLTE, navigation gestures, and it seems that users will also need to decrypt their device before installing. That being said, we’re pretty sure the OnePlus One is no longer eligible for Android updates so if anything, that device will benefit the most from this port.
As for the OnePlus 5 and 5T, Android OEMs typically give devices two years worth of updates so chances of those devices seeing Android Pie is pretty high, but if you can’t wait, then we guess this port could be worth checking out. However given that this is unofficial, we suggest that you proceed with caution and do all the necessary steps like reading up on the instructions and backing up your data before proceeding with it.