Duplicity is not a skill a tank should take under any circumstances. Skills that increase DPS are not necessarily bad to pick up with your extra skill points, but one that requires you not to have aggro is a bad talent. http://www.torhead.com/skill-calc#200MIrokrskbsZZf0cM.2
is generally considered standard, you could move the points in chain shock around, but not to duplicity. Maul shouldn't even be on your quickbar as a tankassin.