After talking to a few Spy mains, I think the YER changes are a nerf to an already underused weapon, because if on paper the numbers seem okay, the -50% cloak drain rate actually leaves you with only 4 seconds (Without l'étranger equipped) of invis, for the most benefit being the silent kill. (Instantly disguising as a slower class is only useful in front of a gun, and most experienced spies would find a way to solf this issue anyways)
4 seconds don't allow you to cover great distances or to position yourself well enough to make a proper good play.
On top of that if you choose to kill a "low" priority target that would else be free somewhere on the flank, you need to sacrifice your whole cloak meter again, or to keep your soldier disguise and sacrifice your mobility.
Either way, you're not going to be as efficient as you could have been with another knife.