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Yes Maruichi is just a brand, you can get cheap Ohira or Takashima for much less and same quality.

Yes you are right there are 2 schools in Japan one is of using Jnat stones with knife and tools where you use a lot of pressure on the stone and particles break very fast under pressure and larger...

Harder stones like Lv5+ is very very hard and if some particle from stone it self get loose they can affect sharpening.

So stone have to be as smooth as possible so bigger particles dont get...