I just got rid of my fiberglass bumper for an authentic MS. Honestly fiberglass is just too fragile for daily use and it was flopping around on the track because it wasn't properly supported (that may be just the way mine was made though, I hope you'll make yours with full bottom bracing and support for all the clips/mount points).

 

IDK about fiberglass... heard some bad things (cracking issues)

 

All the Mazda Motorsports ones are fiberglass. With no problems i seen

 

I have a authentic MS front bumper and its 'PDCPD'...I think its a special kind of plastic; extra high impact resistance.