ΔE 10.7, fair: the same colour family, but not a straight swap. Rust is a little lighter, more saturated than Eshin Grey. They are different kinds of paint: Citadel Eshin Grey is an opaque base/layer paint and Vallejo Rust is a fluorescent or effect paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Rust is a little lighter, more saturated than Eshin Grey. They are different kinds of paint.
The same difference applies the other way round: Eshin Grey is a little darker, 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 Eshin Grey on the colour wheel See Rust on the colour wheel
All matches: Eshin Grey equivalents · Rust equivalents