I watched the videos and think this is a very handy idea...if you are swinging one of those giant 18" coils all day long! No wonder they invented it. But I got no present use for it with my lightweight machine.
I do like the instructional link in the second posters comments...looks fairly cheap and relatively easy to make. And the videos show how to size it for your personal use.
Should work good if you use a harness set up, which I don't.