Questions about polmers and plastics

I am old school and like steel and wood.My background in industrial maintenence has had me use alot of plastic products.My only real app in firearms was the military with an M-16.At the time it was called a Mattel Toy.Now with the proliferation of polymer frames and engineer grade plastics I am lost.I was looking to upgrade the stock on a SKS.I installed a recoil buffer,did the bolt carrier mod and upgrade the firing pin with a spring.I had made comments elsewhere about a polymer stock such as Tapco or ATI and all I got is that it is junk.And these are Glock fans and own AR's with all kind of plastic on them.

My question is how do you tell a quality plastic product from another?The reason is I want a SG Gunworks stock which converts the basic SKS into a bullpup config and shortens the overall length 10 inches.A young ladie does the install video so it cant be that hard( though she is probably really sharp in her field).I know there are some really smart people here so I am looking forward to becoming informed.

I know I spelt polymer wrong in the title-sorry fat fingers and I did preview it

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.

thanks