I now have both and can try them out back-to-back starting next week. I've shot the 180 since 2016 on a D810 then D850 Nauticam housing.
I was able to try a 45 degree finder at the Digital Shootout in Bonaire in June. In July I bought a Z9 and housing for it, and I was told you had to change from a DSLR viewfinder to a ML viewfinder, so the 180 I had would not ... work?
I bought the 45 degree ML, and I'm sure I'll like it for macro. But for wide angle, I'm not so sure. There are a lot of times I take a landscape shot and immediately rotate the camera vertically and get a portrait shot of the same subject. With the 180, this is trivial.
Anyway, I was curious to see if the 180 would fit the Z9 housing, so I tried it. Fits just fine! So I looked closely at the housings just now - the viewfinder mounts are identical!
Maybe the ML viewfinders somehow make the eye-detect monitor/viewfinder swap work, but I don't think so.
At any rate, I have both viewfinders and will find out soon if there are any deficiencies in the DSLR 180 on the ML camera.