There seems to be a fair amount of confusion regarding terms like magnification
as applied to viewfinders. This short article
is consistent with my understanding at least, and provides what I think is a pretty good overview of the subject with clarification of the terms.
In short, coverage
describes what fraction of the scene to be recorded is actually visible through the viewfinder. For example I've discovered that many of the old medium format cameras I like to play around with have surprisingly poor coverage, showing a narrower field of view than what the camera ultimately captures. In addition, the line of sight through the viewfinder may sometimes be off a bit meaning you are effectively mis-pointing from where you want, and they can also be noticeably rotated from what the camera actually sees. These issues are something of a pet peeve of mine since I like to compose fairly precisely, so I sometimes feel like I am shooting with blinders on with these cameras. Of course there's the opposing argument to all of this which says you can always just crop the final result when you're done. so having some margin against clipping the edges of your subject is really a good thing.
really means something completely different from this. It is a measure of how the apparent size of objects appear in the viewfinder relative to their size when viewed directly. The article explains this and other terms in better detail than I would care to try, but I will just say that personally I value full (100%) coverage much more than I value 100% magnification.