I'm running this insert, and I did find that it made a positive difference. I did find that the bike felt more crisp and responsive at partial throttle settings. At full throttle, there is no difference, and if you were either at idle or wide open, I don't think you'd notice a difference. But, if you can ride a KX-500 wide open all the time and never have partial throttle openings, you are my hero (and your last name is Lechein or Ward).