I put a 10 oz Steahly flywheel weight on my kdx200, and I like it. I was afraid that it would slow things waaay down, but it didn't. It still revs quickly, but just a little softer. And it is less prone to stalling in the very tight rocky stuff that I ride.
Ever since I got a trials bike, I gained an understanding of how controllable the powerband and the clutch can be. KDX powerband and clutch are a long way from the feel of my montesa, but the flywheel weight brings it a little closer on the low end where it matters the most to me.
If you ride slow tight stuff with elevation changes - big or little - my experience is that you will love a flywheel weight. Steahly makes the only one for KDX (as far as I know), and he is a super nice guy to deal with. His weight mounts right up. One of the best monies I have spent on my KDX to make it a better trail bike. Everybody that rides my bike with the weight buys one. Cheers John