AAVs may be regulated by local codes, but they are otherwise legal if properly installed. There must be at least one vent to the outside. The AAV can not vent the entire house. Also, the AAV must not be concealed within a wall. Since they are a mechanical device, they can fail so they must remain accessible for replacement. I don't think there is a high failure rate on them so I wouldn't get overly concerned on that point. I think most pros will advise venting to the outside if at all possible, and I would second that unless there were construction issues that made outside venting very costly or difficult. I suggest you discuss local codes with you local authorities before installing. They do work quite well, so if allowed, you ahead.