I' ve had both the Schumo idler kit and Daryl's spring loaded on my KT which has always ran metal tracks.

As to DT's kit, when I installed it with metal tracks, I noticed thatthe track seemed to bunch up just past the drive sprockets. It didn't look well. Upon investigating the problem, I found that on each ilder, the two tension springs (supplied with the kit, and cut to the DT suggested lengths) could not keep the idlers from fully compressing, and consequently, the track from bunching up under the sprocket (due to the heavy weight of the metal track). The problem wasn't terminal, and I partially solved the problem by shortening the springs significantly and by installing an extra spring on each side (the instructions were for an installation with a plastic tracked vehicle). Afterwords, it worked much better (it still bunches up, but I can live with it) and I currently run them on my KT. I"m not sure if DT has redesigned it for use with metal tracks since I bought mine 2 years ago. Like others have experienced, (and despite the bunching) I've never threw a track.

As to the Schumo kit, my experience was with their older design (that was nice and cheap at $27.00 or so) idler system. I found it easy to adjust (set and forget) and rock solid. There was no bunching up of the tracks anywhere. As to digesting rocks, they worked surprisingly great. I found that the narrow space between the track horns allowed pebbles to get in, but the idler crushed them as they went through without a hitch. Go figure. I see Schumo's current model has been redesigned (mine was bought 2 years ago) in typical German fashion, and looks way more complicated, and expensive. I'm guessing that it still works pretty well though.

If I were to do it again, (assuming the same parts as available then) I'd give the nod to the Schumo kit as it comes out of the box. Daryl's are a better design, but weren't well suited to metal tracks during turns or on grass.