Just for grins, I did rappel with one. It gave me a super wedgie, and more significantly, tended to ride up and hinder breathing. But it worked.
I have used mine as a sling in setting up a rappel anchor. They are handy items to have around (your waist).
I have never used mine to rappel on. I figured if I did it would ride up to my floating ribs (like it sounds with what happened with you) and give me the weddgie of a lifetiem. My plan was that if I had to rappel I would do it so that I was slanted down more and thus forcing it on my hips.
But for low angle activities and even just using one to get to a car in a steep ditch to hook up a winch cable the belt pays for itself and proves very very effective.
Humm maybe leg straps would be a cool addition to the belt.. something that hid away untill needed..