LOVE them! have tried the trialtech with two pulleys and thr trialtech with a roller, have tried spokes and Echo SL tensioners aswell.
Trialtech with pulleys: Suuuper tension, its in the way if you want to remove the wheel, It can take a beating, but it dents your frame if you land on it.
Trialtech with roller: Good tension, its in the way if you want to remove the wheel, if you hit it it will bend and the ride is over...
Spokes: Good, hard to manufacture, chain can fall of if riding rough with some speed
Echo SL: Did not work at all. Not enough tension on the spring
74Kingz: Crappy original spring. i have made a spring out of hacksaw blades. just works, and its easy to take of the wheel when you puncture.
So i have bought 2 extra 74kingz tensioners just to have in the future!