Puzzle solved:
Yes, it is for a model "One Step" /"1000" camera.
Fits fine and works fine!
I became doubtful as fitting that flash, seen that photograph, would necessitate to take off that rubber cup at the eyepiece. Not likely for a consumer flash.
So I thought of a Berkey camera as it got no rubber Cup, but still a rectangular eypiece.
But it turned out that the flash had no rectangular ring to fasten it, but a bracket (difference not visible in the photo) to clip on.