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I used Brutal Rust this year on many things, our cemetery fence, lamps, and lab panels. It works very well, and I really like the final product. We did an industrial area in our pallet maze, (1st picture below) some of the areas were large and using Brual Rust was not budget friendly. Those areas I painted in using 4-5 colours of paint with a final touch of using Shellac for a wet appearance.
So in my experience Brutal Rust works well, if you have budget contraints then it's probably not practical on large areas. I have never tried Rust Dust?