I may find the budget for a good chimney later on, but the question is, because this screen has no split prism, only a thin etched crosshair
I'm no sure if the nomenclature but it is a very bright screen.
I can no post pics from phone at the moment but the screen is a fresnel, at an angle, you see concentric machining and clear cross hairs.
There are no notches.
There are no markings.
I suppose this is a third party tool.
Not trying to minimize your concerns. You have come upon a subject about which many people have had issues in the past. The original Hblad screens were known to be dark and difficult to use unless the light level was very bright. I won’t try to get into the whole history of it here, it is well documented if you spend some time doing your due diligence. The Acute Matte series of screens came later and so forth, and were much better.
To your specific question though, I had tried at one point to use a loupe with my Hasselblads and did not like it.
1-unless you get one that will cover the whole focus screen, you won’t be able to see the edges, only the center
2-you have to stay with a lower magnifcation. Too much will only amplify the texture of your screen, and make it harder to judge sharpness. 5x would be max, 3-4 maybe the sweet spot
3-the waist level finder is not that big at the top, so getting a loupe to fit through there is going to be tough. Mine did not fit, and I was going to have to remove the finder to get the loupe onto the focus screen. Not only was that process itself a problem, but once the finder was off now stray light was coming into the focus area as well. The term “one armed paper hanger” comes to mind.
4-A good split image screen is selling for $400-500 these days. They scratch easily. Putting something like like a loupe onto and off of that surface is going to damage it, hindering the sharpness thereafter
5-I have seen those chimney finders for $100 or less. I haven’t looked at them in detail, meaning I’m not sure the price of a nice quality one, but to get a good loupe isn’t free.
I still stand by my original answer to you, I just skipped all of the detail in this post and cut to the chase.
Good luck with your search. I ended up biting the bullet and buying split image screens for all of my bodies because I couldn’t focus reliably with the others.