This thread inspired me to do a little rust prevention testing.
The steel discs found in the photos below were all prepped on the same day according to mfg's recommendations. All discs had the same mount of rust present prior to testing.
A 2 part conversion coating on this disc without media blasting. As you can see, it didn't perform very well since the original rust was never really removed, only "converted".
After media blasting, a 2 stage iron phosphate wash & rinse was applied. To date no corrosion has reformed.
This disc was only media blasted. At first glance you would think this process is working well... until you look at the bottom of the disc in the next photo.