As I'm sure you know given your background, there are good materials and bad materials. There are crappy polymers and good polymers just like there is good steel and bad steel. Some plastics are too fragile or will melt when certain cleaning agents are used or slipped on them.
Regarding the Tapco line of products, I can not comment on them reliably as I have not owned any thing from them but I can say that most items from Tapco I've held and shot did have a cheap feel to them.
Regarding the bull-pup stock, I seem to recall reading multiple reports of them being finicky.