The AAV question arises here periodically, and always brings mixed comments. The simple answer to your question is, yes, the do work and it will vent your sink. The chief objection to them is that they are a mechanical device and therefore can/will fail. For that reason you must leave access to it. You still must have a "real" vent to the outside, which of course, you do. There is no pipe size 1.2". Maybe you're converting 1-1/4" to a rounded off decimal? I'd use 1-1/2" for a utility sink.