My Knowledge of Natural Finishers is Limited to the Arkansas & Escher Thuri..I have Only Recently Got into Natural Finishers..Both these Stones are Great Natural Finishers..The Escher Thuri I have is a Step Up from a Naniwa 12 Super Stone in Terms of Sharpness & Also Mellower on the Face..At a Guess I Would Suggest My Escher Thuri has around a 15 k Finishing Capacity..
My Escher Thuri is Also a Fast Cutter & as Easy & Quick to Use as a Naniwa 12 K Super Stone..My Arkie Surgical Black is a Very Slow Cutter & Without Doubt has a 20 K or 20 K + Finishing Capacity..I Have Found Both these Natural Stones to have around a 99 % Dialled In 1st Hit after Coming Off the Hone..
My Surgical Black is the Most Dynamic Stone in My Books..It has a Wider Grit Rating..8 k to 20 K..It Seems to Perform Well with any Steel I have Hit it with..The Cherry on the Cake is that its a Beautiful & Creative Stone to Use if Perhaps Not a Great Choice for the Professional Honer Due to Time Constraint's..
Billy