My humble answer: We have covered this topic to some extent, and you can read more here. Of the studies done so far regarding the new HFA propellant, it appears it takes the medicine deeper into the lungs than the old CFC propellent and the dry powdered version of inhalers. While studies are ongoing, and so the debate is ongoing, some asthma experts recommend switching to the HFA version of a medicine if you continue to have trouble with your asthma. Personally, I'd recommend trying the DPI first if you have uncontrolled mild-moderate asthma, and then if that doesn't work try the HFA version.
Yet the main reason for making an HFA inhaler, I think, is to provide another option for asthmatics who have trouble generating enough flow to suck in the medicine using a Dry Powder Inhaler. With the HFA inhaler you squirt the device and the flow is automatically generated, and all you have to do is inhaler.
Regardless, studies seem to show the medicine is at least equally as effective as the Advair Diskuss and is another option for us asthmatics to try. For more information regarding the Advair HFA check out this link.