GAP also sells the Super "C" antenna. This thingamajig looks like a CFA
(hoax)
antenna in my eyes...

Well, the CFA "works", and the "C" works. Anything works to an extent. The
CFA works like any short fat vertical, and so does the Super "C". The CFA does
not work as the inventors describe, the C may.
The "C" works 20 meters thru 10 meters, and if you look at the dimensions of
the radiator and ground plane, the efficiency shouldn't be that bad. I have
not measured ,,just guessing. No worse than my 8' mobile antenna on 20-10m.
The "C" should put out a decent signal on 20-10m.
Small antennas have efficiency problems. A "C" on 20M or a CFA of comparable
size and properly matched will work ok on 20, but try them on 80m :-(.
73 Gary N4AST