Get a dedicated viewfinder, unless you own the 24 mm and 28 mm, then get the combo.
The combo is a compromise.
The Voigtländer may be a better solution. I have a dedicated Leica viewfinder for my 24 mm which I'm happy with, but it has a plastic feel to it as well.
Zeiss makes some of the best lenses in the world. I can't imagine they would make a bad viewfinder.