I find more use out of cross-classing the Haymaker ability to my BRD as it's 5th cross-skill, than the Slow effect it adds. I think it was meant to be used more in low level mob fighting, because I could actually tell a difference then. It sort of loses its usefulness when you get to 50.

But Haymaker!!!! I love it! With such high Dex, I dodge stuff all the time. High potency, low TP skill is awesome! /rant