I have one of them - Mentor panorama 18x24 cm. Two years ago price was about 230 $ with 5 DDS.

And yes, it`s a GDR/DDR monorail camera with Zeiss barrel lenses (4,5/300) and behind the lens shutter(1/125 - 2 s).

Mentor has full movements, but it`s quite heavy (11 kg), so I made some modifications and now it weights only 7 kg, so I can take it with me outside in my pocket