I have to tell you, I am not a fan of these "Magic potions". If you are refering to the products such as "POR-15", "Rust Bullet" and the like. However, I have and will use them under certain cercumstances. They are however NOT to be used unless you REALLY need them to "cover up" rust. That is all they are doing is "covering up" the rust, that just isn't a proper repair.
If you are refering to products like Epoxy primer, etch primer, or metal conditioners within a paint line like PPG, DuPont and the like, these are very useful and should be used on bare metal under you paint system.
