Blending Medium vs Matt Varnish

How close are they?

ΔE 7.4, close: similar, with a visible difference side by side. Matt Varnish is a little darker than Blending Medium.

Can I use Matt Varnish instead of Blending Medium?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Matt Varnish is a little darker than Blending Medium.

Can I use Blending Medium instead of Matt Varnish?

The same difference applies the other way round: Blending Medium 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.