Actually Rick, as our historians would point out, it is the plain pot helmet, as worn by the rank and file shown in the third image, that is probably more accurate, as military fashion and helmet design had moved away from the solid full face helmets that tended to make their wearers unable to hear orders, or what was going on around them.
However, it is likely that units of men, going to war, would wear a wide variety of styles of helmets and panoply. Weapons and armour were expensive items and were often treasured heirlooms that had been handed down from father to son. So a phalanx would would not be the neat and tidy and uniform entity that we are obliged to portray with the RTW engine. It would be a riot of shield designs and motifs, helmets, armour and colour. This is something that the Med II engine will allow us to do.
The officer's helmet is actually quite archaic, but he does look rather grand and distinctive, as officers should (

) in it, so our rationale is that he is wearing his grandad's "lucky" helmet into battle.
