I wound up buying the 30-90mm zoom, and while it is very good, I subsequently bought the 45mm and tend to shoot only the prime lenses. The zoom is very versatile, but for my purposes the edges and corners are not sharp enough to be a good general purpose lens. It is better at 30-50mm or so, but at about 60mm and up the lens is quite soft in the edges, and never gets sharp enough that the transition isn't apparent in large prints. Small prints would look fine. Since I am mostly photographing things far away that are mostly equidistant, this behavior is very visible. In a closer range, more 3d environment, this would be much less apparent.
At first I thought it was a problem with my lens or body, but I went on a visit to Leica and brought both, and they looked at them and tested them, and pronounced them both as performing perfectly. The behavior is hinted at in the MTF charts...there is a fairly strong dip in performance at the edges...tangential structures are below 20% contrast at some apertures and focal lengths. If you compare this to the MTF of the 45mm for example, even at 2.8 it barely dips below 40%, and at 5.6 it is all above 60%. In the real world, this means fuzzy edges. If the convenience is more important than edge to edge performance, then get the zoom. If you want the best possible results from a technical standpoint, don't believe the marketing that the zoom is "as good as the prime". It is on center, but not in the field.
The major caveat to all this is that it is still a superbly good lens, just not as superbly good.
You could just cut off the edges!
Here is another photo at 90mm that did not show much of a problem. Most are just fine as long as you don't look too closely or compare them to the primes.