I rode two days with Bill Dart in September, in Idaho and I ran a Michelin trails for the first three days and a Michelin S-12 for the final two days. I rode four different regions of Idaho over the five days. I was extremely impressed with the performance of the trails tire. I was running 13lbs of air and the only problem I had was a couple of pinch flats and it wanders to one side on pavement. Under very hard braking conditions the tire does not slow as well as a knobby, this is where your braking hard with front brake and the rear tire is very light on the ground. This problem is eliminated by just braking a little sooner and transitioning to throttle as you enter the turn. If you brake into the apex of the turn, you will feel more comfortable with a knobby. I spoke to former ISDT rider Mike McGowen and he said that the flats and wandering are eliminated if I run 22 lbs. Bill Dart runs about 8Lbs. The tire performed as good as a new S-12, with a Bib Mouse, in most situations and better often. Especially on loose rocky climbs with some roots and steps. In the Italian Peaks area of Idaho, the Meyers creek trail was quite rocky and very loose. Bill and I waited quite a while for the others to make this climb. I started over a minute behind the last rider. The tire was quite impressive as it found traction where the other riders with good knobbies where working really hard and had to make several runs at the long mountain trail. East Fork Beaver in the Sawtooths was dry and very slippery with several steep switchbacks. I rode up in 2nd and 3rd gear and never had to work the bike to find traction. On the upper part I followed another rider and you could see him working a lot to find traction. This was our first day and he was on a brand new knobby. I ran the Michelin S-12 on days 4 and 5 and I did have to use more body movement to get hooked up than I did with the trials tire. Day five we rode North of Stanley in the Yankee Fork trail system. Rode Cinnabar up top trail 162 which takes you to Custer Lookout. Then down Razorback. Bill said 162 was a really tough hill. I had to work pretty hard to get up that hill where if I had the trials tire on I think it would have been much easier. I ended up backtracking as the other rider was unable to get up 162 with his knobby,so we took trail 163 up to Custer L/O. This is a really "fun" loop for "A" riders. I would love to try it in deep sand, I suspect it will work pretty good as the tire will tend to ride on top, where a knobby spins and digs, I think the trials tire would plain out and stay on top. I did not notice any loss of performance in the few mud bogs I rode. Did not ride enough in sloppy conditions to form an opinion.
The impact to trail is considerably less. I think the price works out as you will get at least three times the mileage. The trails tire will hold up and still perform for over 1000 miles. The bottom line is that I came away very impressed.