Mmmm, after seeing these ads in US comics over many, many years, it finally turned up in our local Magnamail mail order catalogue. My mother agreed to order me one for my birthday (I was about 14 - 1972?), and the result was very underwhelming, especially the tiny box it arrived in! While it appears to be a large, commercial overhead projector (only just starting to become popular in schools in the 70s), it was extremely tiny and required no power source to operate.
The ad misleadingly shows the artists using the device from a distance, but the barely-visible superimposed image you are supposed to trace can only be seen on the paper if you press your eye to the viewer. (Then you can't really control your pencil very well.) Mine had a hairline crack in the base, where the upright pole was supposed to connect, so there was enough wobble to be annoying. When copying a 2D artwork, the source material had to be pinned upside down on a wall. It was hopeless trying to get enough light to fall on a 3D object. The trickiest thing was directing light across the source material to illuminate the image clearly - I spent a long time trying to direct a goosenecked desk lamp at the right angle (that I had to return to to my Dad's desk as soon as possible).
I used the device once, then hid it in a drawer. My old pantograph was definitely more fun.