also add this, urethane is also harder to paint if you do not take the extra time to prep it. if not properly preped it WILL start peeling, unlike fiberglass bodykits.
fiberglass kits weight less then urethane kits. also 10x's less expensive, easier to fix, and easier to mold to the car for that one piece look!
i've order my fiberlgass kit, fenders, & fender flares from racecreations.com they have one of the best pricing & customer service around. all the items i've order had fit prefectly.