You know, I thought I would be more impressed by the ZI viewfinder. After all, I remember with fondness the finder in the Bessa, and the ZI is supposed to be better. However, in practical use, I never felt it put to shame the finder of the M4 (which was recently CLA'd). If anything, the magically disappearing RF patch of the ZI tilts the scale in favor of the rock-solid VF/RF of the Leica.
This is of course based on using a 50 lens. I'm sure that with a 35, the wider space around the ZI framelines woulc come handy, and it's one of the many reasons I'm hesitating.