The difference between using the LiveO2 AC vs the LiveO2 boils down to being able to get your heart rate up enough to give the extra burst of power for the oxygen to go deeper and penetrate/re-oxygenate the body more deeply and efficiently. When you are simply using LiveO2, it has tremendous beneficial effects, but it is limited in its effect in that exercising in the consistently oxygen rich environment of the LiveO2, it is more challenging to get your heart rate up to the point where you are able to take the oxygen most deeply into your system.
For a person who is not at peak health, the LiveO2 may be the ideal system as it allows the person the benefits of EWOT and may be about the maximum someone could handle in a compromised state. For a person who is active and healthy, the ability to get your heart rate higher in the oxygen deprived high altitude environment gives the body the ability to take in the rich oxygen more deeply when alternating between the Adaptive Contrast mode and then back to the LiveO2 mode. Your body, when in the AC mode, is put into an ideal physiological state to then use each molecule of oxygen it takes in more deeply and most efficiently when it is again flooded with oxygen-rich air.