I've just looked on the website for these....(
http://www.sprint-booster.co.uk/)
+ from what I can gather..... they make it so you don't have to press the throttle down as much.
From the website:
"Sprint Booster modifies the signal between the accelerator pedal module and the electronic throttle body. This modified signal forces the throttle body to open 'more' than the stock signal at a given pedal position. In effect, the idle-to-full-throttle pedal travel is reduced. "
The best bit:
"It doesn't add horsepower, but makes the throttle more sensitive and makes the car 'feel' faster."
I think i'll put this one with the Ecotek valve, electric supercharger etc :s