thumbs up on the Mountune splitter! I think both the Mountune and Triple-R are good looking products, but the Mountune one looks just a bit better. It looks like it sits more parallel to the ground than the Triple-R, which is vital to making a splitter work. It sucks for ground clearance, but that is what you need to make it function. I don't think Mountune copied Triple-R since there are only so many ways to make a splitter. It is either flat or raised in the center. That is about it for options.
As for Fiberglass, my dad has had a Fiberglass front air dam and skirts on his Saleen since 1985 and only a few minor cracks around sharper corners. Not bad for a 30 year old car. The key is to avoid parking curbs, steep driveways, jumping your car, or hitting it. I would probably add a strip of polycarbonate on the bottom surface and extend it out a 1/4" or so. That would help protect the FG. Concerning CF vs FG, both crack and can be damaged by impact. The best solution is not to hit anything. If you are prone to hitting things, look at a skid plate instead.