The drive-by-wire accelerator works on voltage about the range between 0.2V at rest and 4.5V at full throttle. However stock accelerator does not generate linear voltage, i.e.: at half throttle, it generates about 1.5V which is way less than the midpoint voltage between 0.2V and 4.5V. This is to smooth out the surge of power when you accelerate.
Sprint booster (SB) boosts up 25-30% voltage when you step on the accelerator. Stepping accelerator with SB at about 25% will give you the effect of stepping about 40-50% of stock accelerator. SB normally generates max voltage at 75% throttle. That is why sprint booster manufacturers claim faster acceleration but does not add more bhp.
Some will argue that you will get the same effect of SB by stepping faster and harder on the stock accelerator and thus save the money.
So it depends on your driving/acceleration style. If you usually increase the throttle smoothly, sprint booster will give you faster and more power surge. If you are already an aggressive accelerator, sprint booster won't help much.