Never saw one before, except pictures. Let's suppose the thing broke while you were toting the tank. It might drop the tank in a way that is not good. That's why we pick them up by the valve.
Other neat gizmos you will run across are the tank banger, the underwater horn, the flashing regulator knob, and various types of artificial spit. I don't have those either.
Mike, the gizmo I have is the worst. The Ikelite waterproof cigarette case. When the BC was new, you could attach this waterproof cylinder to your gear and open it up while floating on the surface. It would contain several cigs and a lighter. Have a smoke while you float. I used it, mostly as a gag while quarry diving. I found out I didn't need those either.
Stu.