You can buy it cheaper and locally as "Concrete Etch and Metal Prep" at Home Depot. It is the active ingredient in rust-converter spray paints and CLR. My de-rusting approach has evolved to wire brush loose rust, soak several days in Evapo-Rust, clean then soak in phosphoric acid to convert remaining rust pits to hard black, then rattle-can metal primer.
I run a large group of fasteners thru same in a glass jar, shaking in a large yogurt jug between with soapy water to knock the loose stuff off, with many rinses. I then paint with black lacquer rattle can. If very pitted, I've just soaked bolts in gear oil. I think that is the treatment for "black oxide" tools like impact sockets. I think they pit the surface with phosphoric acid then soak in thick oil. Aluminum anodizing is similar and can soak in dyes for color. Similar treatments to protect the steel in firearms. Wifey doesn't like the phosphoric acid smell, so only work in the laundry bathroom w/ vent.