Prior to its publication in the Gen, in 1958, Malcolm Davison had been using this, his invention. So
the only date we have for his invention is "prior to 1958."
Unfortunately, its flaw is
still evident - as can be seen in the photo of its entry. That flaw is VERY obvious when its
actually being used by a performer.
This is a case of something being low priced, but still
too expensive. For if it doesn't work, any price is too expensive.