NASON Epoxy Primer/POR-15 Questions

I found a lot of new rust within the areas that I opened up in my last repair cycle , all of it had been professionally prepped and coated with POR15 . I personally will not waste my money on their product again ,the shop that applied it swore by it. I used 2 part epoxy primer on all areas that didn't need welding immediately after stripping to bare metal , weld through primer on those that did require welding and covered everything with a second layer of the epoxy .