I have an IBERA seatpost rack on my Ridgerider. Overall, I like it, but there are a few things about the rack that I dislike:
1. It sits really high and I often hit it with my leg when mounting or dismounting. This might not be as much of a problem with a taller rider who has his seat higher than mine.
2. The seat post clamp stays tight most of the time, but a couple of time it has loosened up while riding on rougher trails and potholed gravel roads.
3. I originally bought the rack to use to two bikes; my Ridgerider and my old commuter bike. After switching between bikes a half a dozen times the threaded bolt started to show wear and I worried that I'd eventually strip the threads. I now just leave in on my Ridgerider.