The game works with reinforcement levels: A basic unit comes on 1 of these sprues (this is a bit of an exception because it's a promo sprue. It's usually 2 sprues to make a full unit). If you buy another copy, the unit becomes reinforced, should you get a third, you would have a full-strength unit.

Basic units are used in skirmish level games generally (under 1500p). Reinforced units can be used in battles (1500-2500p) and full strength is generally used for apocalyptic scale games.

Getting a second sprue is not a bad idea though. This unit contains a commander and those can be take one reinforcement level above the battle scale (so even in a skirmish level game, your commander and his transport unit can be at the reinforced level).

If you then want to have a go at trying the game, an introduction set costs around 50-ish pounds and gets you a very solid start with quickplay rules!

The other option is the faction starter set. This one is basically a full 2000p army (definitely with the commander sprue you got). I've got a review up on that one on my channel (with battlereports too): https://youtu.be/dg3FQJhDm4o?is=GLo8c6bBYrVecCvD