This method of firelighting is a lot older than the 1970s. The vestal fire of Rome and the sacred fire of the Mexicans were obatined by means of reflectors. Scale up the same principle and you have got the Archimedes death ray burning the Roman Fleet at Syracuse around 214 B.C.

As in the book 'Art of Travel' by Francis Galton from 1855 states.

'Black Tinder - Tinder that is black by previous charring or from any other cause, ignites in the sun far sooner than a light-coloured tinder.'

There is nothing at all 'gimmicky' about this method of firelighting. There is of course only one obvious downside to this method of firelighting otherwise there is very little that wears down, runs out of fuel or can mechanically fail within the device itself.