Naaa - not the only camera by far! But maybe the only 35mm camera that is switchable. The half-frame/full-frame concept was pioneered way back in the day, for instance 6x9/4,5x6 folders, or my MOCKBA 5 6x9 folder that can use an insert for 6x6, some of those was switchable in mid-film too. The germans did unbelievable things long before WW2.
But this was interesting I've HEARD of the switchable Autoreflex, now that you remind me of it, but never seen one. I have a Autoreflex though and a few lenses to go with it, I could start looking for a switchable predecessor! Thank you!
PS wasn't there somewhere a version of the later Konicas to be had in half-frame only? I think it could be ordered specially??