The rangefinder on the IIIc is coupled for the
50mm and 35mm, only the 80mm needs to be
focused with the finder to find the distance,
then refocused using the distance scale. It's
ok for still subjects, but certainly not kids. The
80mm is not close focusing anyway, so it's
best for landscapes and the like anyway.
The build quality is fantastic. It's well worth
trying, and should sell for what you paid if it's
not for you.
The IIIS is quite different. Not a folder for one
thing, and it shares lenses with the Retina
Reflex line of SLRs (and Voigtlander DKL), so
the lenses are larger and further away from
the film. Think Leica R vs. M, except these
are limited to 1950s vintage. Still, the
Schneider and Rodenstock glass is fantastic.