This has been answered. Repeatedly. Roughly once a week, in fact, if I recall correctly. Please search and read before posting.
Originally Posted by velocibrad
Pretty sure the comments on Wowhead say that it procs off of rupture/garrote/DP, but yeah, I wouldn't imagine it being more useful than our current best trinkets.
Comments on WoWhead are about as informed and useful as the Rogue class forums on WoW site. I really would not trust the mechanics of anything except how to breath to those comments.
Anyway, I was curious about the 4 piece T7.5; I'm a little lost as to why the 4 piece is beneficial to Mutilate. 3 energy knocked off is cool and all, but on a short fight (see; anything that is is 3 minutes or less) it doesn't seem like you truely get the benefit of the bonus. Is it possible that taking Recluse, Adroit, and Leggings and then 2 pieces of the T7.5 is a better alternative that yields an overall greater benefit?