These clamps are pretty great on my DR-503c. The clamp fits nice and tightly and my Mapex boom arms fit them great. I really love the extra tilter as it obviously adds a nice extra way to position stands either for accessability or to help clean up your setup. I've leant my boom stands back and almost fully extended the boom arms, and it allos for what I think is a cleaner looking setup.
The clamp is very stable, it hasn't slipped on the rack, the tilter hasn't slipped (though you do need to be careful about the positioning of the stands and stuff in the clamps, sometimes they rub against the rack bars, depending on the angles) and the clamp holds my cymbal stands really well.
