Yea, I've been playing with «Dual Stab» altho at a simple lvl 1
Im a bit stuck with my current build (bought a skill point and I heard that if you reset skills you lose it), and its lvl 1, a mere 3% chance, but leaving that aside, the buff it offers lasts for merely 5 seconds.
It might play similar to «Shadow Strike» and «Shadow Explosion»'s combo, but it just doesn't feel the same.
I've managed to use «Moonlight Drive» during the buff effective time and it doesn't deplete, it seems like you can spam «Deadly Blow» for the rest of the time and you'll get the bonus for it too. Might need to test it out... but I can't!!