It makes sense to get the xm18 because you can get the discount and flip it if you don't like it. But after owning 5 or 6 xm18's I definitely like the zt better, both the 0550 and 0560. When I bought my xm's I loved them but back then the zt's weren't around. The 0560 is incredible, easily as good as the xm18 and IMO as good or better machined. The inside of the ti slab is relieved for weight savings, the handles are contoured, the clip is a low rider, the pivot has bearings, the steel is Elmax which is as good as what Rick uses.
The 0560 is a technological powerhouse that has everything the xm would if it were designed today and not years ago, IMO.