I have a large Franconian and I really like it. I've had it for about 3 years now. I read a review on another shaving forum by Harvits81 (Joe Edson, custom razor and knife maker)
http://badgerandblade.com/vb/showthr...ght=franconian
I know that Gabor Buddel, the German custom razor maker rated the Franconian very highly. He finished a Damascus custom that I commissioned from him on one. Super smooth finish.
I've never used an Escher but I've had a few Thuringians and I prefer the Franconian. The one I've got is a large stone which makes using it very easy. I've found it a little slower than the Thuringian but no where near as slow as a C12K.
Maybe the people mining them didn't know what they were cutting, maybe there is a huge variability in them but I'm very happy with mine.