ΔE 19.6, loose: different enough that you should pick on purpose. Aluminium (Metal.) is noticeably lighter than Metallic Medium.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Aluminium (Metal.) is noticeably lighter than Metallic Medium.
The same difference applies the other way round: Metallic Medium is noticeably darker.
ΔE is the colour difference between our two swatch estimates: under 2 is a perfect match (you’d struggle to tell them apart), under 6 very close, under 10 close, under 15 fair, under 20 loose, under 30 very loose, and 30 or more a poor match. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Metallic Medium on the colour wheel See Aluminium (Metal.) on the colour wheel
All matches: Metallic Medium equivalents · Aluminium (Metal.) equivalents