My P80's have been just as reliable as my original Glocks. My first P80 has over 6k rounds of 9mm through it now (reloads, factory, and +p+ hollowpoints to prove it will run them...)
While I understand the sentiment of worrying about reliability in time of need, I don't understand the paranoia of "This gun has been perfectly reliable through xxxx rounds, but since it wasn't made in a factory, it magically won't work in the one instance where I desperately need it..."
I'm not saying that's the logic you are using, but I see it a lot in the anti-80% world.
As for the legality of it, I've talked to firearms attorneys, LEO, and even the ATF, and no one cares as long as you are legally allowed to own firearms and have a valid CC permit.
When I specifically pushed the question of the lack of a serial number, two things were brought up by the LEO and ATF agents.
1. It's no different than carrying a pre 1968 handgun. Perfectly legal, but no serial number.
2. As long as there WASN'T a serial number, that has been removed (missing material, scratched off, otherwise made unreadable) then there isn't an issue.
I expect I will get more questions about it if I ever have to explain it, but until the laws change, there's no issue.