Looking at some suppliers that sell CFG.... They guarantee it for 20 years.
I think you should look at ease of installation of the two. I think the PC is alittle easier too install.
FYI... When calculating how much CFG you'll need... take into account the over-lap if your looking to reduce leaks. On the PC you'll need lapping strips.
polycarbonate is pretty cool stuff, the thickness of it dictates the amount of light that your plants are exposed to, and i think you can get that info easily online.....i looked mine up once and was really impressed.....i still use a shadecloth from march to oct...gl