I have a couple of M's with the 0.58 finder (a Millenium M6 that was converted to 0,58 from its 0,72 and a MP). I am primarily a wide angle user, 21/25/28 and 35 go on the 0.58 with the outside edge of the 28 frame becoming a reasonable 25 frame. The 50mm frame is usable but not great and the 75/90 frames are useless.
Up to and including the 35 it is easy to focus and it is precise enough ( although with the VC 35/1,2 I prefer a 0,72 finder).
The "companion" to the 0,58's is a O,85 M6 as that one will give me a big,bright frame for the 50 and 90, For the 75's i simply use the Bessa R3M as that one has a "free-standing" 75.
What I like about the 0.58 is that for the 35 lenses it will give me a unencumbered set of 35 frame lines and nothing else.
However, if you keep going between 35/75 and only one body, you would be better of with a 0,72 as the 75 is a lens that requires a very deft and precise focus! The 1,4 in particular takes no prisoners - at 1,4 you have a very slim margin of error! The f2 Summicron is better, but to take full advantage of that lens, you want to "hit" it right everytime.