ΔE 4.4, very close: most people won’t see a difference side by side. Outlining Black is a little darker than Matt Black Primer. They are different kinds of paint: Army Painter Matt Black Primer is a technical paint or medium and Nocturna Models Outlining Black is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Yes, for most jobs. Very close match (ΔE 4). Outlining Black is a little darker than Matt Black Primer. They are different kinds of paint.
The same difference applies the other way round: Matt Black Primer is a little 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 Black Primer on the colour wheel See Outlining Black on the colour wheel
All matches: Matt Black Primer equivalents · Outlining Black equivalents