Bras, automobile hood covers, and the like are not things I'm a fan of. They may stop rocks from dinging the nose of your front cap, but don't protect the costly-to-replace windshield. Our 3M film doesn't stop the largest or highest velocity stuff, but does get most of it before the paint takes a hit, and the heavy film rather than the paint gets the swirl marks from washing micro-grit; eventually the plastic can be replaced with paint underneath relatively unscathed.
Bras and the like tend to trap gravel and grit underneath, where it grinds away at the entire painted surface as the material moves above it. Neither system is perfect, but bras... No thanks.
Joel