Theres never been any doubt that phosphoric acid/Ospho works great at removing rust and keeping it gone and also keeping bare metal from rusting.
All the controversy has always been about the paint/primer prep because if the treated metal isn't prepped right the primer wont stick well or will bubble up on you. Even though Ive used it a long time and know how to use it, all this controversy has made me respect the products use much more. I always pick a few spots after its primed and cured and check adhesion by sanding down to the metal, carefully checking how well the metal to primer edge feathers back, it should feather back smoothly without any broken edges. After that I'll try scraping it off in a few spots with a razor scraper if you can scrape it off the metal fairly easily youve got a problem. it will scrape off in little chips but it'll be very difficult and break many blades.
Once you have the proper prep down you'll be able to use Ospho with confidence as a rust remover and metal prep.
As a metal prep on old metal theres also no doubt how well it cleans. Many times Ive prepped metal for epoxy without using ospho by sanding followed wax& grease remover (solvent and water born) then used ospho on a small spot and couldn't believe how much dirt and grime it got off my prepped work.
Ospho is a great product but respect it, prep carefully and always check adhesion once the epoxy is cured and BEFORE moving on, if you screwed it up that's the time to find out NOT after it all painted.