ΔE 16.4, loose: different enough that you should pick on purpose. Demon Red is noticeably lighter, more muted than Pure Red.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Demon Red is noticeably lighter, more muted than Pure Red.
The same difference applies the other way round: Pure Red is noticeably darker, 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.
See Pure Red on the colour wheel See Demon Red on the colour wheel
All matches: Pure Red equivalents · Demon Red equivalents