ΔE 3.8, very close: most people won’t see a difference side by side. Ink White is a little lighter than Matt White Primer. They are different kinds of paint: Army Painter Matt White Primer is a technical paint or medium and Vallejo Ink White is an ink, glaze or transparent 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). Ink White is a little lighter than Matt White Primer. They are different kinds of paint.
The same difference applies the other way round: Matt White Primer is a little darker.
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 White Primer on the colour wheel See Ink White on the colour wheel
All matches: Matt White Primer equivalents · Ink White equivalents