Nobody said it was not good, POR and many other stick like $hit to a blanket.
Some problems have been delaminating etc, but it is a very expensive product. Zero Rust topcoats work well too, but are less money.
I clean up the rust, use Picklex(phos acid), then rusty metal primer shot out of spraygun, and topcoated, works excellent for me.
2k epoxy primer is very good for adhesion and corrosion resistance, but needs topcoating.
Depends on what you are doing, frames, floors, battery trays, etc, POR away, whatver works for you, is whats best........