Look it’s certainly not useless and it’s fun to play around with. But I’d take a second 35mm lens equipped camera any day.
Just the very fact that you have to unmount the lens to collapse the camera tells you something about the ambitions of the designer.
It was an afterthought, later cameras would do better.
The IIIc is perhaps the ultimate fixed lens 135 folder in a long and proud line, where during last stages of the design work, the designer noticed that SLRs, Leicas and Contaxes sold rather well, and got anxious.
The real Retina RF with interchangeable lenses came out just a year later and made a mockery of the IIIc aux lenses.
The mighty Retina IIIS.
View attachment 244355
(image from Cameraquest)
This is how you do changeable lenses on a rangefinder.
It clearly shows just how slow and cumbersome the IIIc lenses where.
In many ways the IIIS is more advanced than the Leica M3.
For example:
Automatic viewfinder adjustment for different focal lengths.
No goggles needed for 35mm.
Due to leaf shutter, flash sync to 500.
Build in light meter.
Sane film loading.