I haven't tried Rust Bullet. Based on their website I have these comments:
1. I am immediately suspicious of companies that spend more time running down the competition than talking about the specifics of their own product.
2. All the talk about "scientific testing", but without any real data makes me question their results. If the testing was so important, publish the results.
3. Some of the claims against POR-15 were a little weak.
a. yes, POR-15 needs a topcoat, but only for cosmetic purposes.
b. the "four step preparation" required for POR-15 makes sense to me. Any product that claims you can just slather it on with no cleaning or etching doesn't inspire my confidence.
4. Without looking at their test methodology, I think their approach to testing 'the main ingredients' in the competitors products is weak. I have done some research into paints and coatings and I know that you can't just test the 'main ingredients', because it is the addditives, modifiers, and other minor ingredients that make a system work or fail.
5. Finally, I like to buy from manufacturers that have their own manufacturing ability, and don't just operate out of a suite in Las Vegas.
I have used POR-15. It takes a bit of preparation. But I have an old-fashioned belief that 90% of the success in a paint job is good preparation.