I'll limit my comments to what I've actually used.

Firstly, I find that rattle cans suit my needs best for applying the dull finish, as I don't like getting out the airbrush after the paint dries. So...I like rattle cans for the dull coat.

I've tried Rust-oleum "frosted glass", and found it didn't work so well . It left an unwanted white sheen on my tanks, no matter how light the coat...especially the darker colors like dark green or olive drab.

I've tried Army Painter anti-shine matte varnish (rattle can), which has nearly zero gloss. It was beautiful, BUT the varnish formulation apparently has the nasty habit of dissolving water slide decals.

I keep coming back to time and again to Testor's Dull Kote. It's a bit too much gloss for my liking, but it dulls with age. It comes in a small sized rattle can, but is handy and reliable and works with decals.