ΔE 15.3, loose: different enough that you should pick on purpose. Flanker Light Blue is much more muted than Gauss Blaster Green.
Can I use Flanker Light Blue instead of Gauss Blaster Green?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Flanker Light Blue is much more muted than Gauss Blaster Green.
Can I use Gauss Blaster Green instead of Flanker Light Blue?
The same difference applies the other way round: Gauss Blaster Green is much 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.