Quote Originally Posted by Revenant
Post Marian legionnaries have +1 to defence, attack and morale, compared to Polybian principes. They also can form testudo formation, have good stamina and they come in units of 100+2 men, compared to 80+2 principes. They are definitely better.
True, but you have to count in the price as well.

Cohors Reformata cost 543 upkeep, which is 5.32 per man.
Polybian Principes cost 342 upkeep, which is 4.17 per man.

So you get something better at a noticeably higher price. It's a decent upgrade, but not a huge difference. In contrast, the upgrade from Camillan to Polybian is a major improvement for both hastati and (especially) principes, IMHO.