I think that the IM should only be able to hear the things spoken by the person he chooses, and not the people talking to him. But even as it is this can sometimes lead to autoguilty if he picks a mafia. Or if the person talks at all, they will likely be mafia.
Mafia will obviously be carefull about what they say if this role is present. Still this might cause good mind games especially with other night meetings.
Yes similar to this role it seems. But the meeting at which the Invisible Man does not have to attend a meeting of Mafia. And must follow the good person to have something to hear.