Has anyone tried these vintage USSR-made planar magnetic headphones?

I see many of these being sold on ebay as "new old stock" essentially. Brand name is "Echo" I believe. Very interesting. Measurements here:

https://reference-audio-analyzer.pro/en/report/hp/echo-tds-16.php#rw35

I find myself tempted to buy one and transplant the drivers into a modern pair of cans and modding it from there... Hell, 3d printing a baffle wouldn't be too hard I bet.

 

I remember those being discussed in the giant ortho thread over at Head-fi many years ago, but actually finding the posts may be trouble.

 

Digest from some russian-speaking forums:
- it is supposed to be clone of Yamaha YH-1;
- most owners are satisfied;
- "easy to listen";
- for "old-ortho sound" lovers;
- generic stock version has no sub-bass, has fast sharp bass, good mids, rolled-off unclear highs, good macro-dynamic, not good details;
- recommended for rock, especially 70-80s, and guitar music;
- Sovet production for non-military purpose - expect huge variations in quality/parameters;
- best made versions were built in Kiev (just physical build quality, not necessary affects sound, actually less pronounced sound signature);
- most owners are modding theirs, various guides available;
- some argue that modding kills unique sound signature;
- some mentioned that >1 hour warm-up is needed before each session;
- some headphones have completely unusable stock pads/dampening due to aging.