the reason is that fibreglass doesn't fit right and needs mods from the body shop. If your car isn't winter driven and you want to save money I'd say do it, otherwise, our winters are too harsh and your front will look like shite the first winter it goes through and will need repainting. Don't forget to put 3m tape or similar which is also bucks, so not really worth it. Buy the real stuff, pay more, but pay once... That quote "You get what you pay for" seems to be poping up all the time...
2001 330ci - Winter beater - RIP
2001 330i - New Winter beater
2004 Carrera 4S - Summer Fun In Da Sun
2005 R1 - Speed Deamon
2006 Civic - New Beater YAY!