Anyone ever used Rustbullet ??

I have used Por 15 over many years now and have found it to be generally a good product, but not to be used in all rusty situations, for example in areas that tend to vibrate or flex a little like fenders or doors...the Por 15 hardens up like glass,which is not good for flexing areas, especially, when you put down 3 coats, and I have also found that rust will creep back under the painted area without me even seeing it, even when there is no rust on the other side of the sheet metal..anyway I am looking for a better product for my situation and was wondering if anybody has ever used rustbullet www.rustbullet.com