The quality of paper used, the typesetting, the cloth binding and in general the physical attributes of their books were a work of art in itself. One can easily fall in love with the physical book just for the way it was designed, let alone the content.
The authors used in their translated works were equally exceptional in their translation.
I fondly remember reading their "Physics for entertainment" by Perelman as a translated work in good old days and it actually made me fall in love with the text book physics taught at the school level.
Given that this was an artifact when USSR made it even more fascinating. Books were priced a trifle over the shipping cost as they were likely subsidized heavily by the government.
It is sad to see that they are no more. They were likely defunded/dissolved when USSR broke up.
Thank you MIR for lighting up my childhood.
RIP.