Someone correct me if I'm wrong, but I think Covenant had a deleted scripted scene showing the Alien killing the Neomorph before getting onboard the ship at the end.
The August 19th draft had a prolonged fight between 2 Neomorphs and a 121. The Alien eventually wins. The novelization has a quick battle in which the Alien just tears the Neomorph apart, much like when the Hybrid/New Beast meets the Alien in Gibson's draft.
Always put your money on the traditional Alien.
£ 101.44 is a lot though.
You can just buy the core book. The rest is all just Gucci.