I am bringing up an old subject.
Sprint booster devices are not only about gas petal response. They send a higher voltage value(*) to the ECU, which is a way of requesting more power. In a sense, they use an indirect method to change the ECU's throttle tables. We made a test once, on a modern Subaru engine, by adjusting directly the throttle mapping tables. We found that there were noticeable performance increases. In fact much more noticeable than playing with the air-fuel ratios. Manufacturers play these days with the engine's inputs and outputs and add in the ECU additional internal parameters. Main reasons are the fuel consumptions and the emission regulations. By changing the throttle table values, you can somehow break these restrictions. Of course, no company that sells such devices will ever admit this. They prefer to say that their devices do not alter the engine's configuration and that they do not break the rules.
(*) It is approximately a 30% increase. For example if the max. value of the ordinary gas petal is 4.5V, then the sprint booster's max. value goes close to 6V.
PS: If someone has already changed the ECU mappings, then the advantages of a spring booster device will be minimal. If someone still see a difference, then it means that the ECU adjustment wasn't optimal
