I spotted the Clarus MS-35 on Jim Eckberg's Flickr stream and asked around on social media about this camera. It turns out these cameras weren't as reliable as the cameras they were pitched against in adverts (Leica?). The shutters seem to break down and the contruction wasn't too great at all. Mark F. O'Brian commented: "great looks, awful construction. Few of them ever worked properly!"
It also seems the Clarus MS-35 was essentially a copy of the Perfex 33.
Introduced immediately after World War II, The Clarus (essentially a copy of the Perfex 33) was featured in full-page ads comparing it favorably with the Leica. In spite of its simple mechanical design, sturdy construction, decent lens and clean styling, the camera was awkward to hold and quickly developed a reputation for unreliability. It could make good pictures when its shutter would operate properly, but unfortunately in early examples this almost never happened. Models made after 1949 can still be found in working order, although accurate shutter speeds are too much to ask even of these.