PU material is definitely better and more durable but having said that unless it's genuine parts, which we all know are mega expensive, there is no guarantee that the fit is any better than fiberglass. If budget is a concern then fiberglass is obviously the way to go.
I am in no way connected with the vehicle bodywork trade but the pics below show that if you take your time, are prepared to take the kit off and out it back on, again and again, making small adjustments where required until you get the fit bang on, then the fit can be as good as OE.
Time must be taken to make sure that the the fixings used are up to the job and you use enough of them, unlike the car in the you tube video, how that kit ever stayed on at high speed is beyond me!!
Using the correct fittings and enough of them will reduce the amount of flex the fiberglass goes through and thus there is a lot less risk of cracking.
To sum up, for me the cost of PU was out of the question, so lots of hours getting the fit right, when your happy, take just the kit to the paint shop, get it painted then enjoy fitting the kit to your pride and joy for the last time and take pleasure in the fact the kit cost a fraction of the PU option but looks just as good. OH!! and be carefull near the Kerbs LoL
During the fit, not good enough yet!
Rear bumper complete
Front, rear and side skirts, fitted painted and a personal sense of acheivement.