Not recommended to use anything below 2.5 on a slim 510. But Tornado is an EGo-alike and could use the 2.4 though I heard they are more likely to crack if you are buying the old totally clear CE2 clearomizers.
Gotvape shas early CE3 ones with thicker tube, supposed to be less likely to break. They are still calling them CE2 Fluxomizers (their name for the Clearomizers) but added Deluxe (probably beta CE3)