Hi
These kits don't affect power or the engine in any way.
It just speed up the response of the accelerator pedal.
It does make the car feel quicker, in effect the kit is shortening the time taken for the engine to respond to the throttle position.
I must admit that I was tempted to try one of these.
The one thing I like is the ability to set it to different responses or even switch it off and make it act as standard.
I have heard of people years ago just fitting lighter throttle springs in their (pre-electronic) cars to give a more responsive feel.
I also heard of people putting on firmer springs to gain economy by slowing down the acceleration rate.
It is surprising just how much difference the spring rating makes, a loose spring can make the car feel very sporty and a stiff spring can make the car feel sluggish (and improve economy)
That is how this kit works to, but not via a spring, just by changing the electronic signals.
So the theory is fine and I am pretty sure that these things do make the car feel as if it is driving differently.
I still might try one just to see if I like it.
Steve B