The "silver rich" part was marketing.OK, so the whole silver thing with Efke was purley marketing?
I know a few people were saddened when Efke closed, and all i would hear from them was about it being the last plant that made "high" silver content film lol
The old emulsions, spectral sensitivity, contrast, grain, reciprocity behavior etc. was what it was. Some people liked it, and amongst those people it was popular.
IIRC, in some parts of the world it was also inexpensive. People liked that.
Their IR sensitive material was also relatively unique in the market at the end. People liked that.
But mostly, I think people were unhappy that something they appreciated was going away forever. I understand that - I still have a little bit of Plus-X that I will miss when I've shot and developed it all.

(Opera lover here)

