Astorath Red vs Red Oxide

How close are they?

ΔE 15.2, loose: different enough that you should pick on purpose. Red Oxide is noticeably darker, more muted than Astorath Red.

Can I use Red Oxide instead of Astorath Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Red Oxide is noticeably darker, more muted than Astorath Red.

Can I use Astorath Red instead of Red Oxide?

The same difference applies the other way round: Astorath Red is noticeably lighter, more saturated.

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.