I've been hearing reports that in the other versions of the game that this is actually increases sneak attack damage. Testing will show which of the two it is eventually.
SE really why oh why you do this?
I so hope that they are planning they are going to make a trial that you can add Roque's Armlets +1 and this hands into one so you will have
increase "Trick attack" damage
increase "Sneak attack" damage
and other stats ofcourse