I shaved this morning with the Razor (pre) finished with the Naniwa Gouken Fuji 8K. (see a couple of posts above).

Got a very nice & smooth shave. Sincerely, couldn't say it was made with a synth stone. At least, it wasn't harsh how some people reports. Maybe it wasn't the closest ever, but easy & smooth for sure.

I'll have to test this stone deeper (as Eucid440 suggested), but it seems to have a big potential.