Well, for starters know exactly how invisibility works for both PvE and PvP. In PvE, so long as you don't double jump or bump into anyone they can't see you. They'll still flail their arms to swat at the area they last saw you at if they were pursuing you, so note that. Think Gorgons if you've done VoG, that's stealth in a nutshell. In PvP, it takes you off the radar so long as you don't sprint. Most people can spot a cloaked figure nowadays thanks to the Silent Fang and Taken Minotaurs, but they won't be able to see you coming if you're out of sight AND off the radar. And if you want to nail that instant kill backstab, you want to make sure you're both. Think of it as an "off the radar" ability as opposed to a "they can't see me" one. Also noteworthy, the backstab effect doesn't proc on shielded PvE enemies. So take that shield down/have a fireteam member take that shield down before moving for the kill. The main disadvantage of KS is the fact that if you're a Gunslinger (like I was) you need two seconds of crouching still before you can even get invisibility, and if you're a Bladedancer you have to either put up with that or you need to stab someone before you can be invisible, both of which leave you very vulnerable in some form or another and delay your ability to coordinate your backstabs against those pesky shielded enemies. This is why I am REALLY looking forward to the Year 2 return of Khepri's Sting. Escape Artist will basically give you invisibility the second you need it, and Shadestep can quickly close gaps and get you behind the enemy swiftly. I'm already practicing a Shadestep maneuver to run at a target then pop an Escape Artist smoke bomb and Shadestep around them so when the Shadestep ends I'm facing the enemy's back to deliver a backstab. It can be done, I've pulled it off a few times, but I need to be able to do it at will. (I know, "NERRRRRRRRRRRRRD!")