We've tried them but none of us really like them much. We do, however, have one on stage at all times in case someone in the crowd wants to make an announcement.
Steve, you know far more about 'tech' than I do... with newer equipment they've done something that helps prevent feedback haven't they? I ask because feedback used to be a major problem for us, so much so that we got a feedback eliminator. But today we VERY seldom get feedback... and no longer use the eliminator. If we do get feedback it's 'user error'... one of us has done something stupid.