I think the real issue with the Barnack viewfinders is not that they are "squinty" but that most kinds of lens hoods intrude into the viewfinder image for 50mm. That alone favors the use of auxiliary finders. I have not seen 50mm finders with parallax corrections, but there are many 35mm and 90mm finders that have a crude but effective manual correction in the form of levers that will tilt the finder for closer ranges. I really enjoy shooting with a IIIf, but the Barnacks definitely require slower shooting than more advanced cameras. The exception to this may be using wide angle lenses with much depth of field, and print film with lots of latitude for imprecise light settings, so you can virtually skip the focusing and metering steps.