Olyfa as a brand date back to about 1930. They made low quality but expensive razors.
When it was offered to me it was the first Olyfa Réglable that I had come across, but since found a reference to them on a French forum.
Its a four piece, made of Zamak andf is basically a "flip plate" razor, but unlike other flip plate razors, this one's plate is completely internal.
Adjustability is via, what could loosely be called a shim, which in turn fits into a machined section. There is a square raised section on the base plate and a corresponding recess in the flip plate. The gap is determined by which side is facing upwards. The last image in the second row shows both sides of the adjuster plate.

How does it shave? Been a Flip Plate, it has only two settings. On its lower setting its reasonably aggressive. Flipping the plate over to its higher setting its wild and ranks within my top 10 aggressive razors.