So several times on late game guns, I've been keeping around groups of Legionary units as a sort of melee bumrush unit.
Well, for the first time I actually got upgraded shields, and oh man does this change the poor rookies from bumrush initiation fodder to an actually effective group.
Panic is a hilarious problem, as are flanks, but considering these guys are basically just going out praying to survive and get promoted, this works well.