I want the sharpest image with the least distortion, and for the prices they're charging I want these qualities across the entire frame. These Z SLR lenses seem to be highly center-optimized, some more than others. I don't want to make it sound like they suck. Not at all. Just that only one or two of them offer a meaningful image quality improvement over the equivalent focal lengths available from Canon/Nikon, and they are expensive. What I will say though is on the subject of flare/ghosting, Zeiss always excels. T* is still the best coating out there in my opinion. The other thing I'll agree on is the mechanics and build quality are excellent. They are a joy to hold and use.
But if people want them I'm happy to part with my 25mm and 50mm, barely used, mint condition ZFs.