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Apples & oranges.
You simply have to test each stone to see its merits.

No. This is why a lot of us use diamond plates ,because the base stone is finer than any Nagura but not everyone has uber fine base stone which makes opinions vary.

2 reasons a DMT will scratch the stone.
1. It has high spots. These will create irregular patterning (See pic with obvious circled areas)
2. The stone is not "well" worn.

A well worn DMT C...

So you say Nakayama trumps all other mines then you say its like a 1970's Ford Mustang ? Wakarimasen. :thinking:

Actually, as an ex mechanic I'd say it's more like Datsun 1600 rally car with...

Here is a small Nakayama Maruka Asagi with all stamps.

No way to definitively tell provenance of this stone.

Just generalising here:
The best acting stone should not cost more than $1k approx. Hiigher cost will be aesthetics weight ,size etc.
A razor stone will also help keep the price down. ie roughly...

You cannot tell from pictures how a stone will perform in your hands but Hatanaka san is known for top shelf stones, not just Maruka stamped ones.
That does not make unstamped stones inferior.