Meopta Focusing Aid at Film Stage

Was this or a similar aid ever used by other manufacturers?

So, what is it? A grid or resolution target like item that goes in place of the negative to give a known-sharp image to focus?

No, the Meopta aid is is substitute image that woud have to be assessed in the same way.
Instead it consists of two staggered edges within the film stage (being of use when the stage is pulled forward) that project two images of slits onto the paper plane that at focus overlap, forming a thin line.

Optically a bit different , but in effect similar o the split-wedge aid.

t

Durst "NEGA"

I forgot about that one...
However the Durst aid is of the kind Donald has referred to: a substitute, static image (target) projected.

Gnome enlargers, English made, although this was back in the 1960@s, it was the first proper enlarger I ever owned, and their ''Rnagefinder'' (their own description)