Actually I think snake rekon said they're just for show. Damage per second doesn't matter when everyone has 50 Hp because there's a slight invincibility phase between hits. Very slight but when the difference of damage is only 1 it doesn't matter anyways. When hitting a vault at a gang base, it may matter. But when you say it's quite a lot faster, I have to disagree. I've seen them used and the speed is nearly the same as other daggers.