This old staple still doesn't have a review?
Testless damage is always good, and this one is a huge upgrade. While Sneak Attack (0) requires you to pass an evade*, this one doesn't as long as the enemy is engaged on someone else. That saves you a test and an action most of the time. Two testless damage that can hit aloof enemies is excellent. Chuck Fergus makes it fast and allows it to be used on other players turns, too. An auto-include in any Chuck deck and a generally strong event that Sefina Rousseau usually wants.
When it comes to contributing to fights, I've always felt it appropriate that this and Backstab are so much stronger than any of the rogue guns. That's how a Rogue's supposed to fight, after all — not head on, but sneaking in a punch while the 's got them distracted. Save your hands for picking locks and strange gizmos, don't try to be a worse guardian!*
* unless you use it in the player window after enemy attacks with Chuck Fergus.
** unless you're Tony, in which case you're actually secretly a Guardian