Are you sure it isn't better? At first glance, the Penetration looked ridiculously better. Mine is only at level 1 though.
Well, I am comparing a AR Piercing Mod V to a Velocity Barrel I, and I know it'll get better at V but not sure by how much. If it's much better and just tears through armor and cover then it would be worth it on my Turian Ghost where cool down as as much of an issue.
Actually, I have the new barrel at IV. I need to check again when I get home on what the values are. Upon first glance I wasn't impressed but I'm sure I read it wrong.