I finally filled a missing link in my Asahi collection with this AP or "Original Pentax." I ended up with a second body when one was described as a "Pentax S" - but wasn't.
This model has no mechanism to stop down the lens automatically, so uses preset lenses like the Asahiflex - but in M42 mount. (Auto lenses can be used in manual mode.)
Both have very nice cosmetics, but the second curtain on one has stiffened. Although many have said that can't be repaired now, Eric says he can still replace them, so it will be off to him this week.
The other one operates perfectly - shutter speeds good and very even exposure edge to edge. A big difference shooting one of these compared to an Asahiflex with waist-level finder. I find for normal shooting the Asahiflex is best used as "scale-focus" with it's second eye-level viewfinder.
Without the diaphragm stop-down stuff these are simpler mechanically and also quieter.