First of all if you are using the anesthesia machine it is very difficult to incorporate your anesthetic agent with the ambu bag ventilation while easier to do with the hand bag ventilation.

2. Using the bag ventilation helps you to give exact minute volumes by regulating the flows and keping them at what minute ventilation parameters desired by you, with an ambu bag it is difficult to regulate it as you have to then squeeze it just as much required which might be difficult

3. Ambu bag is a non collapsible bag so the resistance might be higher for ventilation as it also has a fish mouth valve attached to it.

4. As far as ventilating on air is concerend ambu bag is a much better bag as you dont need any flows as it is a non collapsible bag, while for bag ventilation you need some kind of flow meter attached to it

5. Ambu bag is good for resuscitaion purposes and in an emergency situtaion.