The idea is, once this gets out, and a few *******s get caught because of it, serious rapists will start checking before hand. This might require them to be more aggressive, and if they find it, upping the violence another notch as retaliation.
It's not a matter of not knowing, it's a matter of thinking of checking first.
The company marketing this is going to push the whole "stick this up there, and you'll be safe." crap.
Well, lets be blunt. To rape you, I have to attack you. It won't stop my attack. You're already going to have been attacked, stripped, possibly beaten up. And, you're still going to be forcibly violated. It won't jump out on me, I have to be inside of you, for this to work. It might make me easier to find later, but you'll still have been raped.
Oh, the risk might stop more casual and random rape, and cut back on some date-rape situations.
But the serious rapist, who stalks his prey, who lies in wait on bike trails and jogging paths...he'll have something along with his duct tape, gag, rope and knife to test for traps. When you deal with guys who will shave all body hair, wear a condom, and rubber gloves...what's it really to spend $10 for a rubber dicky to keep from getting their gear snagged in a bastard-trap?