Nobody likes just having the bare minimum for something. "Well, it's just enough to get by." isn't something people like to say or admit to. Having double the amount gives you a lot more options and flexibility and just generally makes things more pleasant. It's with that in mind that Spartan Games has reinstated their Double Helix Deals over in their webshop.
A Core Helix box has the minimum number of models to field a Core Helix. Meanwhile, a full Core Helix is 2x that amount. So if you get two sets, you can field the minimum, maximum, or anywhere in-between for your helixes (... helixi?... helixees?) for Firestorm Planetfall. Simply buy two and get 20% off. Simple as that.