My main experience is it is with the 2 wheel dollies we use for deliveries. Everytime they show some rust I hit it with Ospho and that's it. It's only once a year that I strip them down and repaint. Same thing with my bike and motorcycle.

We also use it on the boats at TMM to remove rust stains from stainless steel stanchions and then wipe it off. No need to repaint.

If you were applying it to a greased surface I could see where you would run into problems if it wasn't thoroughly degreased first.