That thing just adjusts the voltage output of the stock accelerator pedal sensor, so a small movement of the accelerator pedal will cause a larger voltage to be applied to the ECU input and hence cause a larger throttle plate movement for a smaller accelerator pedal input change.
This may give you the impression that the car has more power or acceleration, but the simple fact is that it's not going to produce any more power or torque than if you just were more aggressive with the standard setup.
The ecu has (say) a 0 to 5v input and this is interpreted as the accelerator pedal movement say 0v is no throttle and 5v is full throttle. Your device can adjust the rate of change of this voltage, but putting more than 5v onto this input of the ECU achieves nothing as the ecu has already interpreted it as 100% throttle application at 5v so feeding 6v or 8v into it achieves nil.
This device can't enable your engine produce any more power or torque, it just changes the "feel" of the throttle pedal to make it appear more responsive.
If you're prepared to pay $300 for something which only changes the way the accelerator pedal responds then by all means buy one; just don't be fooled into thinking you'll get any more power out of this, because you won't. The only thing it will increase is your fuel consumption.
IIRC @
UFI has looked at similar devices in the past and reckons you could build something with the same functionality using an arduino for about a tenth of the price.