This is the most versatile riser block I've used with my Kurt Kinetic Road Machine trainer. The lowest channel in the CycleOps riser block leaves the bike sitting level. The other two channels give slight inclines. There are 3 different ways to use 2 blocks together if you want a plethora of steeper inclines to choose from. You can nest/spoon them together, stack them "offset" as in the photo, or stack them with the bases interlocked together (bottom one upside-down, top one right-side-up) to simulate the really steep climbs. Pretty smart design, I think.
I like the way this riser block cradles the front tire. You know riding the trainer is going to wear your rear tire, but why should the front tire take any abuse? This is one of the reasons I chose the CycleOps over the Kurt "riser ring", which looked like it might abrade the front tire after a winter of spinning.
I'd give it a 5th star if it were a little cheaper.