The way it works is it plugs into your electronic throttle. As you press your foot down depending on how far you push the pedal directly relates to how much throttle your engine is given. Fitting one of these, as I understand it, basically gets rid of this gradual adjustment and gives you full throttle only, at the small touch of your pedal. So it then becomes pretty hard to drive daily, steady smooth slow driving becomes much harder. Great for the drag strip where your foot's planted anyway, but day to day I'd imagine a bit of a pain to live with, unless you permanently drive it like you stole it! So personally, wouldn't fancy it. Talked to the guys at awesome gti about these too, and even though they sell them, for normal use it got a thumbs down, especially for 100ish quid!
Hope this is some help.