ΔE 10.9, fair: the same colour family, but not a straight swap. N5 Neutral Gray is noticeably darker than Matt Grey Primer. They are different kinds of paint: Army Painter Matt Grey Primer is a technical paint or medium and Golden N5 Neutral Gray is an opaque base/layer 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). N5 Neutral Gray is noticeably darker than Matt Grey Primer. They are different kinds of paint.
The same difference applies the other way round: Matt Grey Primer is noticeably lighter.
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 Matt Grey Primer on the colour wheel See N5 Neutral Gray on the colour wheel
All matches: Matt Grey Primer equivalents · N5 Neutral Gray equivalents