I remember seeing something about this a while ago but don't know how it works.
I assume that it's a sort of cheap focussing spotlight, with the light hitting what is in effect a condensor lens, and against the flat side of that lens goes either a gobo or some sort of transparency?
If so, I still have (somewhere) a full size version sold by Elinchrom (don't know who actually made it) and this came with a few gobos, and of course hundreds more were available from 3rd parties. These gobos were made from stainless steel, very thin, and projected a very sharp image (if required, but could also be de-focussed) and there were also some gobos stamped out of mild steel, these were just a series of different sized holes, a bit like Waterhouse Stops, again these focussed.
And there were sliding shuts, which allowed control of the shape of the light, for example if I needed to light the label on a wine bottle I could adjust the shuts to fit the exact shape.
You mention light loss. It's just a drawback of the design, very little light actually passes through to the gobo or whatever and reaches the subject, the vast majority just gets absorbed by the black interior. In fact, to get a usable amount of light at 100 ISO I normally fitted the head from my Chic 2 generator unit, 2400Ws....
As I no longer have any Elinchrom flashes I don't use it anymore, but it was a good bit of kit in its day, and essential pre-digital, when everything had to be absolutely right in camera.