I mained assassin previous tests.
If you're in motion you are more visible. If you're still you are damn near fully invisible. If you shoot you leave invisibility. If you go into smoke you get invis back.
It can create some amazing outplay moments if people are dumb enough to try to fight you in smoked out areas. I'd throw a ton of nades into smoke areas if I know an assassin is there and recon isn't on my team.
I generally used mine to disengage not engage. If a fight is going south and I'm going to get rushed, then pop smoke invis and go reposition to heal up or just GTFO entirely.