Not being a woman, and not having to live in fear of being raped every day, it's kinda difficult to comment, in a way, I think it is a good idea, if nothing more than a deterrent, if rapists knew that their victim might be wearing one of these, it would certainly put them off.
As for increased violence if women used these... difficult to say, yes, there may be cases of that, and cases of this being abused as well, but then, what else can be done, rape is really a massive problem in Africa, it's intrinsically linked with Women's Rights and the protection afforded to them, which is minimal if any. There is the real core for change, but that takes a long long time, and these women are suffering right now.