I don't have a problem with capos in general. I just don't like them on mandolin. Cuts back on the ring too much, which is the essential tonal quality of the instrument. I haven't had a chance to try most of the recommended varieties--actually don't know which ones I may have tried.

But if you can't play cleanly in B flat, try practicing more, or use the capo that works for you, not slagging people who have a different approach than you do.   

A lot of times I prefer the sound of a capoed guitar to the same guitar without one--fewer overtones make it cleaner and crisper. But I've been getting into jazz where weird keys are part of the game, and part of the essential sound.

W-O