Lollipop Magenta vs Crimson

How close are they?

ΔE 6.7, close: similar, with a visible difference side by side. Crimson is a little lighter than Lollipop Magenta.

Can I use Crimson instead of Lollipop Magenta?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Crimson is a little lighter than Lollipop Magenta.

Can I use Lollipop Magenta instead of Crimson?

The same difference applies the other way round: Lollipop Magenta is a little darker.

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.