Well, Think I can answer this one for you. Plus Chris is probably out getting knockered up like most us Americans today, and you wouldn't want to read (or be able to) what he had to say anyway.
First this just replaces the bumper cover not the real bumper. The real bumper is a hard plastic honeycomb peice under the cover. If you ever see pictures of a wrecked Contour the covers don't tend to hold up that well to impact. Since it's ABS plastic it deforms rips and breaks when you hit something.
Second it would depend on which cover you bought. If you bought the Fiberglass it is very hard and brittle. So hitting anything will likely crack it. Also running over the curbs or parking space ends the original bumper covers give quite a bit and just scratch but with a fiberglass bumper you can kiss it good by. Ask anyone with a mirko splitter who's hit something lately.
Now the Carbon Fiber is somewhat of a different story. It is very durable but still hard and brittle. If I where to hit something in say a Mclaren F1 at 60MPH It would likely destroy the front of the car but I'd still be able to drive it away. This is because the whole body shell is made of Carbon fiber. While is still cracks and breaks, it takes a hell of alot more force to do this because it's a woven fiber and not a loose fiber.
So Fiberglass is likely to shatter like galss upon hitting something, where as carbon fiber is more likely to absorb more of the impact and then deteriorate, but as far as being worse in a front end collision they are all likely to be about the same.
