Oh yes, you have been hearing it, they are marketing lies. The web is full of this talk about the magic potions.
There is NO such thing as something that will keep the rust away for ever, NO such thing. The best you can get is to etch prime and epoxy over that. Or etch prime and certain urethane primers over it. Then apply your top coat or base coat over that.
The thing is pick the paint company you plan on using, PPG, DuPont, Sherwin Williams, what ever. Then use the COMPLETE system they offer.
There are some products like Zero Rust and POR, that offer great products to apply over rust that can't be cleaned properly or where you just want to save time. But under your paint on the outside of the vehicle it is not a good choice.
I personally have a 72 VW bug with a rusted floor. I will be using POR on it instead of "doing it right" by sand blasting and etch priming. It just isn't worth it to me with this car to do it right. The POR will do just fine and it will last and look good enough for my little bug.
But on the outside, etch primer, urethane, sanding and base/clear.
