modern 4strokes seem to have a slight bog/hesitation down low. its barely noticable but when you install this, it pretty much gets rid of it. i had the original QS on my RMZ450 and i noticed alittle bit of an improved response. its worth the cash but its not as night/day as the package makes it out to be.
but its an easy install. throw it on and back you airscrew out 1/4 of a turn and it should be good.