I just upgraded from a flat bar hybrid (Trek 7.3 FX) to a road bike (Orbea Aqua Dama) and I love my new bike except for the fact that I have to take a backpack instead of my panniers. Not only is it very uncomfortable (I can't seem to get the backpack to stay centered on my back!) but it's also not waterproof, and in the Pacific NW that's no good...

I looked at a few different rack options, quickly discovered that I shouldn't consider putting a seatpost mounted rack on my carbon fiber seatpost and the best solution I could find is a couple Delta racks that can be mounted to little rubberized clamps that go around your frame. (Amazon has a good picture of the rack mounted on these)

My question is this- has anyone used these clamps for their racks? Do they work with (more or less) any bike rack, or would I have to get one of the Delta racks? Any downside to using these (slippage, load capacity, etc.)?