I have the Back on Track mesh sheet that I used on my OTTB and i absolutely love it. I think my mare did to. I HIGHLY recommend it. She never displayed signs of a sore back or anything like that, but I could tell a difference in her when I used it versus when I didn't use it.
i just bought a BoT "mini blanket" for humans, for myself. I really like it & saw results on the second day. I sleep on it & am waking with much less stiffness through my lower back and hips. While this may just be a placebo effect, the fact that ALL of the cats want to lie on it makes me think that it is definitely doing something.
I am going to get the mesh sheet for my horse. I haven't heard anything bad at all; the only negatives have been doubting the efficacy of the product, especially given the price. It sounds like It won't hurt, and has high potential to help.