I used Hercos for a year back in the Seventies but stopped.
Since then I've stuck with regular celluloid. Heavy 346 triangle imprinted with the band's logo back in the 80s, when I ordered 'em ten gross at a time to toss out to the crowd. Then heavy standard 351 shape for years, and more recently mediums in the same standard shape.
I got two bags of various assorted materials and shapes from another player last year, intending to try them out for tone and see how they suit with my own hand & picking style. Never got around to it. One of these days.
But I am interested, especially about their sound properties.
It's an aspect of guitar tone that I never explored.