True I guess we all draw our own lines in the sand. B50 or FF, all those fibers are synthetic. I don't know that a sinew string would work on this bow, the grooves are tailor made for a skinny FF string.
Tony's "line" prevents him from making backed bows, other than sinewed. In a way I think he's getting better at what he's doing by focusing on a particular design, whereas I branch out so much I never remember what I learned from the last given style I worked on. I'm having fun though.