I assume the rubber in the Cambium flexes more than the leather of the B17 Imp, and I imagine it's more comfortable.

I'm on a tight budget, so I first tried the TRK for it's low cost - maybe $50 at Amazon, IIRC. A year or 2 ago, Backcountry/Comp Cyclist had a sale on some of the higher end versions. I tried out a Glider, I think, and it didn't work at all. My guess is that for the SMPs, the sit-bones to pubic arch measurement is critical. If you look at their patent application, the sensitive bits are supposed to hang out over the nose. The distance from the bottom of the dip to the nose for the Glider was too long, so it didn't solve my specific numbness problem. The TRK fits me, even though I dislike the heavy padding.