Got it on the bug, saved my about £1000 a year until it packed up. I could fix it for under £20, it's just not worth the hassle at the moment since the car'll be mothballed soon-
-Power was lower. Not annoyingly lower, but it was.
-Cost about 2/3 of the price to run, fuel wise
-Didn't notice any difference in sound
-No engine issues- in fact, drove it for the best part of a year on LPG only because I couldn't be bothered to sort out a blocked jet and it was annoying me.
-Installed in June 2013, have since completed approx. 80-90,000 miles* without issue, No valves have burned out (junkyard engine too, which I'd already covered 30K with! Still runs a treat)
-Makes a cool noise when you refuel
*I think that deserves a separate mention TBH. 80K+ in three years on a '73 bug. It's a little champion.
I'd do it again in a heartbeat.