Evaporust is pretty good, IME. The one exception is you never want to partially submerge something in it. If you do, at the water line, oxygen from the air will re-oxidize the iron, and Evaporust will remove the oxidized iron in an ongoing process that will gradually eat into the workpiece along that line. Also, when you have long exposure to it, such as an overnight soak, which they recommend for rust thicker than about 3/16" deep, you can get some slight surface etching. I expect this is the result of the same process at work as when not fully submerging. Dissolved oxygen in the solution oxidizes the cleaned surface iron, and the Evaporust removes it. The effect seems to vary with the alloy being de-rusted. Anyway, if you degrease your part and follow the instructions to check after 20 minutes, and keep checking so you don't use it longer than is strictly necessary, there shouldn't be a problem. It's not like dropping something into an acid. The chelating chemistry very selectively only attacks iron oxides, and it captures the iron atoms that were in it.