Yes it does work!
But if there is rust it will not stop it, but it will slow it down. I don't know principal of how it prevents rust. There is many brands out there but there is a few that work, but what these electronic rust prevention products do is send electrical current through out the whole body whatevers connects to ground of the body, it been used in boats for many years and now its on the automotive market using the same principals as the boats.