Well there's a reason they picked ARMA III over Squad. From what I understand, games in ARMA III are more like tabletop. It's less forgiving and more realistic, with custom missions. I'm not familiar with Squad (though it looks quite nice) so I can't make too many comments on it, but that seems to be my understanding of it. Still, the Mod is a first true stab at large-scale 40k battles. And with ARMA III on sale for $13 until the end of Thursday, you can't really go wrong.