I enjoy zone focusing with an Industar 50-2 on my Spotmatic. Actually, that is really the only way to enjoy using that lens because it has a fully manual, one-ring iris – on an SLR lens! Stopped down to about f/8 it was pretty easy to focus by the scale only. I did check my composition in the viewfinder, but that was about it.
I'll try shooting without using the viewfinder at all next time. Shutter speed is pretty easy to set and forget at daytime (Sunny 16 all day! ...literally)