Having seen their use in stage musicals (also those belt/strap transmitters for guitarists so they're not wired into the amps direct) I've wondered why they're not more widely used. Cost? Picking up local taxi transmissions? Quality? Would they work for a harmonica player attached to his neck harness? The ones musical artistes use seem no bigger than a cotton bud, makes one wonder why stage mikes are still so big if there isn't a quality issue. I suppose a non-playing singer likes to work a hand or stick mike like a prop but I would have thought a multi-instrumentalist who has to move around a bit might find all those trailing wires a hazard (despite acres of duct tape) which radio mike/amp would avoid.
RtS (Not a performer, just naively curious, ie pig-ignorant).