So far I haven't found anything about it on the net, and it's not listed in my 1995 McKeown's. Bentzin was another minor German manufacturer based in Dresden prior to WWII. After the war, as with the other Dresdeners, they ended up in East Germany, ultimately becoming part of VEB Pentacon.
Bentzin appeared to like the "Primar" name and made a number of cameras with variations on that name, none of which look like mine. The Primar Folding camera here, for instance, bears no resemblance to mine at all.
So when did it come out? I think it's post-WW2 because it's got a self-erecting front standard. Self-erecting means that when you open the camera, the front lens pops up into place without any further effort. Prior to this, you'd open the door and lock in place, then reach in and pull the lens standard out and click that into place. Self-erecting folders (e.g. my Agfa Billy, Adox Sport, Voigtlander Bessa, and Kodak Tourist) show up after the war. But the earliest patent I found was from 1929, so this could be pre-war.
Another argument for pre-war is that it has a Hugo Meyer Trioplan lens set in a Compur shutter. Meyer was located in Gorlitz which was East German, but Compur was in Munich (West Germany). Also the little pull-tab on the door (which doubles as a leg when the camera is set vertically on a table) just says "Germany." So I figure pre-war, but just.
It's got a 10cm Meyer ƒ4.5 Trioplan in a Compur with max 1/250th speed. No flash synch.
The camera was imported to the USA by American Mimosa.