The ART 20 vs Koetsu Urushi Wajima is not a End Sound difference I am able to comment on.
Where there is room to comment is on the designs used.
The 20 uses a Titanium and Aluminium and a Elastomer to control resonance produced.
The Wajima uses Rosewood and Urushi Lacquer to create the controls for produce resonance.
Both share Boron Materials for the Cantilever.
The Wajima has a Silver Plating on Copper for the Coil Wire, whereas the ART has PC OCC as the Coil Wire.
There is enough going on in the differences of the Bodies and Coil Wire to suggest a presentation with noticeable sonic differences are able to be created.
Individuals evolve in their attachment to End Sound that has an attraction to them.
I am not attracted to Richness of Tone, and as I have experienced with a selection of Audio Devices, there are certain designs that have this as their inherent trait.
Koetsu Cart's having been heard as a demo' across the years have always displayed quite discernibly a Richness of Tone. How present that is depends on whether the Demo' is supported by Valve Amp's and Horns or SS and ESL's.
In today's worlds there are easier options to experience a Sub Par Demo', but tonal differences between Cart' Designs are reasonably easy to discern, and a Koetsu in a Wood Body is always leaning towards the description of being Tonally Rich.
Another die hard Koetsu user who posts on this forum and has experiences of Koetsu's into the mutli-thousand dollar area, has recently revealed their usage of a Cart' not expected of them to adopt, being an Optical Design as a Phono Cartridge. I am keen to see what they bring to the table as an assessment.
My own experiences of the main Brands Optical Cart's, where Cart's have been demo'd up to the most expensive models. Is that Richness of Tone, is not the first sonic trait that comes to mind for being discernible. This could also be influenced by generator design, as there are versions of the generators appearing in the market place?

