David if something doesn't add to your show then it detracts.
A microphone should be an invisible prop used to enhance a performance. Having a big handheld mic around your neck does not add anything to the show. (Other than making you look dumb
If you need to use both hands then get the AV guys to give you a lapel mic (clip-on mic). And always have another handheld mic with a stand for the audience members to use.
I have to disagree with your statements, Benji. A microphone need not be invisible. If a performer is properly entertaining his/her audience, a visible mic is pretty much not an issue.
Secondly, if you watched the link to the video that the original poster provided, you'll see that even though you may have considered the mic around the performer's neck to look "dumb", the audience didn't seem to mind, nor were they distracted. This was a comedy magic show, and the mic around the neck , though some may find it silly looking, actually seemed to fit in with Mr. Cass' performance style.
Third, you suggest if a performer needs both hands that they should ask the AV staff for a lapel mic. Lapel mics, while practically invisible, are a sound man's nightmare. Particularly if the performer wearing it moves around a lot onstage. The pick up on most is terrible, plus these particular mics a more prone to feedback than most others.
In the book Maximum Entertainment, the use of hand held microphones is preferred overall. It's a good idea for magicians to be able to do their act with a hand held microphone in a mic stand and with a Gim-Crack holder for effects that require more freedom of movement by the performer.
Just speakin' from experience here.