In other words, if you feel the bumper cover that the stock MX6 has, that's similar to urothane. It's like a semi hard rubber. The erebuni kits and TC kits are fiberglass, hard fiberglass. This means that if you get into a 10mph accident with the urothane kit, it will most likely just bend and pop back out. If you do the same with the other erebuni kits, the kit will crack into pieces.
Moral of the story: Don't hit anything with your car.