I just had a look through both finders.
the frame size seems very similar.
I say "seems" because it's difficult to compare.
the VC has a crazy distortion, and thicker frame lines.
The ZI finder is much better in terms of distortion, but the frames kept disappearing (inside, bad lighting), and again, are too close to the 25. they are also smaller, in the sens that the 25 on the ZI and the 28 VC form an almost full rectangle (why leave these small open segments
). The 28 in the ZI finder is more of the "4 corners" type. Add to that the marks for close up parallax correction, and you get an image that may be correct in theory, but is kind of difficult to "read".
Completely unrelated (but if I am already at it...) the ZI, once mounted on a Leica, will hide the speed in use on the speed dial.
It's a beautiful finder, but has too many quirks for my taste...