ΔE 9.8, close: similar, with a visible difference side by side. Brown is more saturated than Rust Tone. They are different kinds of paint: Army Painter Rust Tone is a wash/shade and Green Stuff World Brown is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Brown is more saturated than Rust Tone. They are different kinds of paint.
The same difference applies the other way round: Rust Tone is more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Rust Tone on the colour wheel See Brown on the colour wheel
All matches: Rust Tone equivalents · Brown equivalents