I have been lusting after this Chosera 10,000 stone for some time to complete my Chosera collection (400, 1k, 3k, 5k). I was originally planning on getting this in December from my brother in law who lives in Tokyo but I established that the premium for buying it here was not that much so I bit the bullet and it arrived today.
They are clearly trying to present this as a premium product with that packaging and stone markings being very different from the others. Mine is about 32mm tall and has no base (I never minded the base on the others). The synthetic nagura is that same as the other four I got with the other choceras.
I have been doing a lot of work on my Takeda 270mm gyuto and was pretty pleased with where I had got it to (finishing on Sigma Power 10k + 0.3m 3M paper). Anyway I flattened the chocera with XXC and smoothed the surface with the nagura. I went back down to 5k and then up to the new 10k. A few observations:
1) Polish - fantastic bright finish. Far more than the Sigma Power. I don't have a SS10k so can't compare with that
2) Feel - really wonderful. Completely different from my SS8k (very soft) and SS12k (very hard). Just great feedback. No hint of possible gouging but still giving real feedback. I like the feel of all the choceras but this is the best (followed by 3k)
3) Edge - staggering. Far, far sharper than I have been able to achieve with any other finishing stone. I used the 0.3m 3M paper afterwards and didn't notice much difference
Yes, it's expensive and unnecessary but what a stone.