I wouldn't say that there's no effort on the part of the user. Yes, all you have to do is breathe, but the purpose of the acapella is to vibrate the airways and shake the mucus loose, allowing the user to cough it out. The benefit of the acapella is that it actually strengthens the lungs because you have to force air into the device. There are resistance settings, too, to make it easier or more difficult to get the correct vibration.
I love it and wouldn't use anything else.