I'm currently running one on my CRF 450 and it is the cats meow. The thing is great, I honestly can't say enough good about it. Tight hill climb stuff is a snap, it also still allows for engine braking. If you dump your bike, it will still keep running, just get it upright and ride away. It does have a couple advantages over the more costly Rev-Loc too.
Give them a call directly if you want more info about it. They spent a lot of time on the phone with me and answered all the questions I had. I also opted for the clutch override option so you can still use the clutch if you like, although the pull is greatly reduced.
If they are coming out with one for the KX5 I'll be in line for one, that's for sure.