The Sprint Booster sure looks like snake oil to me.

It appears to do nothing more than remap the response of the throttle relative to the position of the accelerator pedal so that the throttle opens faster at the beginning of the pedal travel. This is nothing you couldn't accomplish on your own, simply by pressing the pedal faster. It's not surprising that it has the unpleasant side effect of making fine modulation of the throttle at low speeds difficult.