The finder arrived earlier today, and to my surprise I can see all four corners with almost no eye/head movement at all, even with the rubber eyecup. I think the image is a little smaller though, making it harder to tell if the bricks in my "infinity view" are as in focus as they could be even after adjusting the eyepiece of the angle finder. I get the impression that removing the eyecup helps give a better idea of whether the angle finder has been adjusted properly, although that could be psychological.
Having the angle finder in place does give back the feeling of being on a wobbly boat that you get from a WLF, so if you're nostalgic for that help is at hand! 🙂
I'm presuming it's a "Mamiya Right Angle Finder Model 2" and not a "Mamiya Finder N". It's got a metal facing at the bottom bit which slides onto the eyepiece of the prism. In the manual, it looks like there is no metal facing bit, and there is a Mamiya right angle finder that doesn't have a metal facing bit, but from the tiny bit I've read, the prism eyepieces for the Super and Pro are bigger or wider than the earlier models so I presume an "N" wouldn't fit.
One thing that is similar to the zorki 4k, is that every time I use the angle finder, I'll have to re-adjust the dioptre correction as there's no way of "locking" it in place. Mind you, with a 4k you just need a bit of sellotape, and then remember to replace it occasionally.