From what I have deduced that it was used in some lab or something. The seller told me that she has obtained it in inherence - she herself had a Ph. D, so that might explain why these boards are pretty much impossible to obtain. (only smart people get keyboards with many keys)
The build quality is pretty solid, little lighter than my grey badge model M. Pretty much no flex on the chassis. Also, it uses a 25 pin connector.
There are two completely adjustive screw feet. The bottom part seems flimsy at first but that is the intention.
There are 2 kinds of switches, Marquardt tactile, Marquardt tactile with LED. Bot of them feel pretty much the same, maybe the larger keys like REPEAT feel bit more tactile for some reason. But the tactility is hard to find in these switches. They more or so feel like Gateron browns, very scratchy.
It has lasered PBT(not sure) tombstone keycaps with interesting symbols. Fairly thick but with no engraving F and J keys. It makes it very hard to type on, even though I'm far from a touch-typist. They are Cherry compatible (I think, they can be damaged by using Cherry switches, I feel like they sit way too tight).
Hinanawi Tenshi Series 44 20cm for size comparison.
Special thanks to HerbalNekoTea#0573 for helping me identify the switch.
Let me know if I can provide more information.