I had a test of the expensive one a couple of years ago (thanx to Daniel at TRAX).
Floored it without and floored it with. No difference. Thanks, have it back!!
It can not predict you are going to accelerate before you hit the pedal, so it wont reduce turbo lag. It can not send more than 5 volts full throttle to the ECU.
It can make 1/4 pedal feel like 3/4 pedal. OOH AAH this FEELS really powerful. but i can do the same thing with my foot. And chirp the muddies..
Anyway, if it feels good, buy it..