This talent is a sustained ability, but behaves somewhat like an active ability, as well. It is sustained in that it is a continual action that is not passive, yet active in that the character cannot perform other actions while in this mode and melees enemies.
There is a bug with this talent where it doesn't show in the list of available talents in Tactics. (Though it is possible that this is intended: in game this talent is classified as a sustained talent which you can activate or deactivate against a particular target, but you cannot use sustained abilities against particular hostile targets.)
pcps3xbox360 If a rogue uses this talent some bosses like the Architect and the Baroness tend to copy the movement. This happens even if they don't carry dual wielding weapons.
The hits can still be critical hits even if the target is not bleeding from twin strikes.