I cant compare it to any other final polish stone but so far the naniwa 12k has worked perfect for me, it has to be lapped first thing because it's got a sandy/rough finish to it but after a quick lapping it becomes super smooth and flat, and its super smooth when you sharpen with it, no scraping noise or pulling, it's to the point it seems like nothing is happening but after about 10 strokes the blade has a super shiny mirror polish. also since its new stock the company changed the color of the material so you get a ceramic looking white stone instead of that weird salmon pink color in SRD's picture.

so I was super happy with my purchase and I'm thinking of getting the naniwa 8k because of how good the quality of the 12k was, also its cheaper than the 8k Norton
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also there is a 12k Chinese stone people seem to have good results with and its super cheap if cost is an issue but its apparently a slow cutter.
Buy Natural Water Stone 8 x 2-3 4 x 1-1 4 at Woodcraft