It's situational and personal preference also matter. I personally love being able to spam finishers when needed rather than missing one and getting stuck without energy for a bit. Also, the 20% really matters; if you roll with a healer it's the cherry on top of the icing.
It's not da bezt talent out dere, but if you feel like you'd want it, I'd say give it a go.
Edit: Also, yes, it only affects finishers. Aka Envenom, Eviscerate, Rupture, Expose Armor, Kidney Shot, and Slice & Dice.
Edited, Oct 19th 2008 11:25pm by Mozared