ΔE 21.5, loose: different enough that you should pick on purpose. Ironbreaker is noticeably darker than Fairy Dust.
Can I use Ironbreaker instead of Fairy Dust?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Ironbreaker is noticeably darker than Fairy Dust.
Can I use Fairy Dust instead of Ironbreaker?
The same difference applies the other way round: Fairy Dust is noticeably 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.