So, I get that epoxy resins are "stronger", but I can't help but wonder what are the drawbacks of cheap-o polyester fuselages/molded parts? For example the old Byron stuff that still hangs around. Sure, it's got some bonding and gluing issues, but beyond that, what makes it such an anathema for kits? Does it really fatigue that quick?

POLYESTER IS FINE .
bonding problem was caused by not removing- WAX- from inside fuse, or parts. clean and don' use-- C/A . epoxy works fine .
EPOXY GIVES YOU, ADJUSTABLE, WORK TIMES .
life span is 100 years ! lol

I would think that Poly could be a little more brittle than epoxy but that said I have a very old eurosport with hundreds of flights and a very old YA F18 twin both poly and no problems with either. The Epoxy can also be made lighter.