My buddy and I did the switch mod for the three round burst. Neat idea but having used both, I figure full auto was better. I almost always fire in quick little 3 or 4 round bursts anyway but when someone goes running across an opening at distance and you need to fire into his lane, having full auto is a definitely plus. On the other hand you can get something like full auto just by pulling the trigger quickly in three round burst
It's not a hard mod at all if you don't mind soldering but it is a delicate and expensive piece of electronics if you're not so good at it.