I hate to rain on your guys parade but I hate those things. I want to modulate my own clutch, throttle and brakes. It can't get much nastier than PNW woods and I am a way better rider for not having one. Flame away all you like, I might not be fast and I certainly don't race, but when the trail gets nasty I'll be hookin up by flexin my left pointer finger while you rekluse dudes are smokin clutch plates!
Additionally I know of a couple tarils I would not take someone with a rekluse down, unless they have a hand brake.
http://www.youtube.com/watch?v=chBPe88f5ns