Simply put: If you have a medium format SLR, what kind of finder do you use? Prism, Waist level, Sports? Something I'm not familiar with?
With 645 and 6x7-6x9 cameras, waist level finders are less useful due to the clumsiness of turning the camera for portrait orientation (unless you have a rotating back like the RB67). With all medium format cameras, prism finders are large and heavy.
When I worked with the Hasselblad 500CM, I had WLF, magnifying Chimney finder, and 45 degree prism. The shape and control layout on the camera made WLF and chimney finders easy to work with; prisms were good, best once I fitted a side grip.
I had prism finders for Mamiya C330 and Rolleiflex TLRs, but used them rarely due to their size and weight. With either, a pistol grip was pretty much essential for good stability hand-held.
With the Hasselblad SWC, I use the groundglass back for critical focus on copy stand and on tripod setups. I switch between chimney finder and 45 degree prism depending on the subject matter and the situation. Speed of operation and proper orientation of the ground glass are obviously of little concern with this camera used this way... you're not going to be racing through a set up anyway.
When I had the Mamiya 645 1000S camera, I had both prism and waist level finders. Never used the waist level, it was simply too clumsy in use. The prism worked well, especially with the pistol grip.
G