Unfortunately it's called misleading advertising. Most of the mod shops record their GTA IV demo video down a dark alley, with no other game characters arouna and only 1-2 guys in an on-line match. The reality is that rapidfire just doesn't work that well on GTA IV due to game lag. There's nothing a rapidfire controller can do to save that.
Originally we did not list GTA IV as a supported game. After getting tired of hearing this "omg, xyz mod shop supports GTA IV but Viking doesn't" we added GTA IV to our 'all in one' driver line-up and included GTA IV in our game demo video.
Go to 6:38 in this video.
http://www.youtube.com/watch?v=LAXQAryoeR0
Notice we're shooting down a side-alley with no game characters around, like every other mod shops' demo video. It's the same problem with jitter mod. Jitter mod *sounds* awesome, in practicality jitter mod is only useful for a some guns in certain situations.
But again, if you do see a video where someone is kicking butt in the middle of game lag with 20 players around, I would be interested in seeing it so we can study it and try to duplicate it. That's the beauty of the USB upgradability - if something is discovered for a game after we release our drivers, it's pretty easy to just re-release them a second time. (or third time.. or fourth time