Gamma did a video on these. He felt they were a reconstituted stone. Results weren't too good if I recall.
I think the Cnat most people refer to is the Guanxi River Hone which used to be sold at Woodcraft, also known as CHUG, PHIG, C12K, etc. The stone above isn't that.
https://www.amazon.de/gp/product/B07CXMZTQP/ref=ox_sc_act_title_1?smid=A3MWTOW3Y5FBF1&psc=1 They are supposed to be 10000 grit but they are quite cheap. Are they any good?