CorrectI have both the Sprint Booster and the JB4. The Sprint Booster really makes the car feel more responsive off the line as a result of the "compressed" throttle input. It makes the car feel like it has more power, but it doesn't. The JB4 actually improves HP and TQ, and is most noticeable in the 3k+ RPM range. Personally I run both. I keep the SB off in the winter, and set to Sport-7 in the summer.
Sprint booster for increased acceleration
JB4 for increased power
I’m happy with just the sprint booster right now! Maybe one day I’ll install the JB4