I've never taken a 30mm hit and lived, that I know of, in fighters. I did take a 37mm hit in a Spit XIV and live once (radiator got holed), but 30mm do a right proper job on me.
I haven't used the 30mm enough to really comment, but in my limited experience it works. I have a couple memorable 30mm kills. I do know that there was a bug that effectively caused duds. Hopefully it hasn't been brought back to life.