I don't know anything about the JB tunes for NA engines, so I shouldn't give advice on selection. I have a sprint booster on my M3 and enjoy using it. It doesn't revolutionize the car, but it enhances my driving experience. It isn't a cheap tune by any means.
It will make the engine feel more responsive without adding power, it just opens the throttle much faster and without a delay. It does make the car "feel" more powerful. You could also add something like an aFe air filter for a small increase in power and a much better engine sound for not a lot of cash.
I find the sprint booster makes gear changes smoother for me, but this will differ with driving style.
I use mine on the street and turn it off when I track. I have an M3 which has 3 throttle maps with M-Drive that can do a similar function.
"To suffer the penalty of too much haste, which is too little speed." - Plato