I'm familiar with other German cameras; I just got a 'folder' that looks similar to your camera. It seems to me that early 20th century German made cameras weren't common in the US; I haven't found much info. about specific cameras (like mine) from that era.
I did a brief search and found mention of a Periskop lens by Steinheil. Often the lens & shutter assembly was manufactured by a different company than the body. If it is a Steinheil or a lens by one of the other German companies it could be an excellent lens. I have a camera w/a Zeiss Teleskop lens (another good German brand) so it could be that more than one company made lenses using similar names.
I also ran across mention of the Orionwerk cameras on the site I linked below; I've used the site before but as you'll see it's not in English and my high school French only gets me so far! Yours looks to me most like the 79 or the 82(A). As best I can tell, it says the majority of models used the common name Rio, with a letter that indicates the format of the apparatus (size of the negative produced by the camera - presumably on 120 film) -
A is 4.5 x 6 cm, B is 5 x7.5, C is 6 x 9 cm, and D is 6.5 x 11 (which is a fairly large negative for a rollfilm camera).
I noticed your camera has a 5 and a 7 on it but I don't know if that indicates the film/negative size or not; it might for that model with that shutter and lens assembly. It could be that your particular camera model wasn't marketed in France or Europe and was maybe just sold in Germany, and that only a certain number were made with the Periskop.
I got an antique camera that has some rust on what I think is an aluminum interior (it looks like the inside of a tin can!). I haven't taken pictures with mine but expect the rust won't keep it from being usable although in a less antique camera I'd be more likely not to buy one with rust. The older the camera the more likely I'll just leave well enough alone. To clean/dust it I usually use a small soft brush made to clean lenses, or gently wipe w/a microfiber cloth (breathing on the lens to keep dry particles from scratching the lens).
If it seems to be in working order I'd probably try some film in it and see how it turns out.
Sharon
edit - There used to be a camera guide by Mckeown but it seems like the last edition was several years ago and I don't think it's in print any longer; maybe you could find a copy at the library?