The Add On men with the lorica hamata and spanglehelms have potential, but are kind of a mess, in my opinion. They could be auxiliary infantry, but they have greaves and pilums, so that doesn't work. Of course the latter is an easy switch, but the former is not. They could be late Republican legionaries, but there's the issue with the greaves again and their shields are wrong for this function. I've decided to make them auxiliary cavalrymen and have equipped them with long lances and Gallic helmets. Although greaves were rare with cavalrymen, it makes more sense than keeping them as infantrymen.
The helmet included with these Add On men isn't quite right either, as it could be, sort of, either a late Republican or late Empire (when it was falling apart) helmet, but it has no ear and face guards, so it ends up looking more medieval. I've decided not to use these helmets at all with my Romans (except for the Hamian archers) and instead I have given them to my "barbarians" to wear.