Using this would leave you completely vulnerable and unable to attack while controlling the 'bug'. If an observant player sees it, you're dead. If someone happens to run in the room behind you, you're dead. It'd be quicker to run in where you want to go (with the new item you can store in the free slot that doesn't contain the "Spy Bot") and shoot everything in there, and you're in full control of yourself.
Plus, if a server had it or gave teams a "Spy Bot", I'd know and be looking out for people using it... and the free kills I can get because of that.