ΔE 16.2, loose: different enough that you should pick on purpose. Fluor Orange is noticeably lighter, warmer than Astorath Red. They are different kinds of paint: Citadel Astorath Red is an opaque base/layer paint and Green Stuff World Fluor Orange is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Fluor Orange is noticeably lighter, warmer than Astorath Red. They are different kinds of paint.
The same difference applies the other way round: Astorath Red is noticeably darker, 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.
See Astorath Red on the colour wheel See Fluor Orange on the colour wheel
All matches: Astorath Red equivalents · Fluor Orange equivalents