[Callers] microphones

Hi all - I'm considering a wireless headset mic. It sure would be nice to have hands free when demonstrating, teaching the introductory workshop. But I don't see many callers using them. Is there a downside to this that I'm not seeing, or is it just the expense? And if someone could recommend a good one, I would appreciate it as I know NOTHING. Our local sound guy has recommended the SHURE brand, but doesn't know a specific model number. Also, what are your thoughts about using a monitor? We have a visiting caller that SCREAMS into the mic and it was suggested that if he had a monitor, he might not do that. Any help is appreciated! JoLaine