Hi Rob,
I can only speak from my experience. Hydrochloric or phosphoric acid has been in every effective rust remover I've encountered previously. I don't know what would be in Evapo-rust that would otherwise dissolve the oxidized iron. I can't get it in Australia so I have not had a chance to try it.
With regard to sandpaper, it works well enough for me. If I want a cleaner job, I use a friend's blasting cabinet with peanut shells or a little Black Beauty for an abrasive.
As far as purchasing Nital, I tried hard to get some when living in the U.S. about ten years ago. Must have called a dozen suppliers and they all told me the same thing. I had to be a metallurgist, an engineer, or a chemist to get any sent to me. I eventually persuaded a chemist friend at the University where I worked to get some for me. The highest strength that would be sent by post was 2%, because it was considered unstable and an explosive hazard at 5% and above. It's also a strong acid, classified as a hazardous material, which is another red flag for postal and parcel services. Since commercial amounts of Nital were in 2%, 5%, or possibly 10% concentrations, the strongest they were allowed to send via post or parcel was 2%.
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