Squig Orange vs Transparent Red Iron Oxide

How close are they?

ΔE 16.8, loose: different enough that you should pick on purpose. Transparent Red Iron Oxide is much more saturated, warmer than Squig Orange.

Can I use Transparent Red Iron Oxide instead of Squig Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Transparent Red Iron Oxide is much more saturated, warmer than Squig Orange.

Can I use Squig Orange instead of Transparent Red Iron Oxide?

The same difference applies the other way round: Squig Orange is much more muted, cooler.

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.