Nylon is not nearly as strong as polyc and shouldn't be used for dueling as far as I'm aware. It just looks better.
Have you used it? Or are you basing on what you heard?
I HAVE used it many a time and had no issues. I don't gorilla duel, but I don't hit super light either. From experience in saber combat (oh, just 8 years, lol) I have tried pretty much every single blade type there is, and when I say that nylon is safe, I know what I am talking about. ;)
Nylon blades don't give that "light in the tube" effect like polcarb does, so the look is indeed different. Both are equally cool.