Anything that goes inline with the electronic gas-pedal's signal and modifies it can't overcome the fact that the ECU limits your throttle at lower RPMs - only tuning the ECU can affect that. What the "pedal-box" type units *can* do is change the shape of the response curve of the pedal itself, e.g. put the 50% mark down at 20%, so that you get more response out of less foot movement, or vice-versa. Ultimately, anything the pedal box can do, your foot can do as well if you move it differently (e.g. stomp gas faster, or use the pedal more precisely). And then of course there's temps vs fueling in the ECU, and the yaw sensor hack, as noted by BGTV8 above
Mostly, I tend to view the pedal-box type things as psychological in nature. You could make the car do the same thing with more foot movement, but the car feels more "edgy" if you barely move your foot and lots of things happen quickly.