yes it seems kinda invincible but off course it isn't.... kishi hasn't shown weakness of any of itachi's arsenal like totsuka, yata or even Tsykumio... n i know KA is shisui's jutsu but we only saw others use it i.e itachi and danzo.....
i think it's a manipulative jutsu with which you can only manipulate opponent until he isn't aware of jutsu like mifune wasn't... hence you cannot give command to kill yourself to your opponent.. n i know of itachi's case but itachi wanted to be manipulated hence that doesn't contradict my theory either...