The Case for [Fleeting Expertise]

Maximizing Ability Efficiency at the expense of Ability Duration is more effective than not. With it on this build, Invisibility lasts for 26.52 seconds and costs 12.5 Energy per cast. While under the effects of Invisibility you will regenerate 15.912 Energy thanks to [Energy Siphon], functionally allowing you to continue casting Invisibility for as long as you'd like.

On the other hand, without it Invisibility lasts for 33.72 seconds and costs 35 Energy per cast. While under its effects you will regain 20.232 Energy. Unlike the build with it, this means that you run an Energy deficit every time you cast.

So go forward with your infinite invisibility. Scan Kavats, I guess?