Clear protecting bras

[JetBlack_GT]

I was surfin the web earlier and I saw an add for those Clear bras that protect your car from rock chips and stuff like that. Are they worth the money? I was lookin at the psooibilities of gettin one but I don't wanna waste my money on it if they suck. Which ones are better than others and what should i look for in them if i decide to get one. thanks
Brian