Having had a carbon shaft, you can DEFINATELY feel the "on/off/on" throttle response impove. However, mine was a bucket and the amount of vibration that was going through the car was rediculous. IF the company could totally 3000000% garuntee that it wouldn't be unbalanced, i'd buy another one and try again.
Torqline in the UK seem to get a good wrap. I know God_Speed has one on his NUR and there isn't an issue.