when i bought my turbo look front bumper it was fibre glass too, so i re-sold it and just stuck with good old plastic.
I never even took the bumper out the box and it was already chipped. I dont like the idea of fibre glass. If i knew it was that i wouldnt have bought it, i thought it was a plastic one..
It all depends on what you want your car to look like, no doubt they look great...
Mind i do like the look of the GT2 bumper... looks good!
www.essentialstyling.com do a kit also for UK owners.