So how does this set itself apart from BF or Arma?
Well, Battlefield is a pure arcade game, this is focused on realism and tactical play. ArmA's 'public' lobby community is non-existent, the server browser is just full of "LIFE" and Wasteland missions as far as the eye can see. Playing tactically, even round based PvP action requires a clan of some description usually. Even when you find one, they seem more focused on playing versus the AI in co-op missions
SQUAD is focused on multiplayer, round-based PvP combat on large maps with lots of tactical elements. I'd really suggest you look into Project Reality for BF2, it was beyond amazing when everything clicked the even the public community was extremely tactical, very helpful and voice was the cornerstone of the game.
So SQUAD kinda sits in between all these games, with a more focused versus based multiplayer mode that can actually be done publicly. Hopefully the PR community carries over. Anyone who played BF2's PR can attest to the fact that it was an extremely special experience with a very mature community.
So it's a continuation of Project Reality in UE4, where they are in complete control rather than at the mercy of what the BF2 engine allowed, plus a nice visual bump.