I happen to have three of those: one standalone NOS chip and two on Q-Bus SBCs. One however has a crack in its cerdip package. Here's what one of the boards looks like: http://blog.funcall.org/hadrware%20vintage%20pdp/2017/03/14/... Boards like these were used both in DVK systems and in different CNC controllers.
I used DVK for a while and yes good chunk of that time was used to play Tetris ;)
Yep they weren't exactly uncommon but generally were installed at various institutions and professional schools: there was no legal way to obtain one privately. They were also (due to peculiarities of militarized planned economy) ridiculously overbuilt and costly to make. It's rather hard to find a complete DVK on the market now as most of them were reprocessed for their very substantial content of precious metals.
A factory in my hometown used to have CNC mills with these systems as controllers and they were regularly pilfered by the socialist workers. The backplane had insane amounts of gold plating (grams!) on edge connectors and boards themselves used platinum/palladium capacitors for bypass! These were stripped on the SBC specimen in my blog post above too.
