Bionaire Cool Mist

This particular model or most of Bionaire Cool Mist models are evaporative version of the humidifier. That means, it uses a fan to create active air flow through a "filter" that wicks water up into a large surface are to generate humid air. Very very primitive way to generate humidity. Plus you need to change out the filter every so often because the filter loses its water absorbing ability.
Ultrasonic version of humidifiers vibrate water molecules and separate them apart and create water mist. This is by far more active way of creating humidity and this process is much more quiet. No filter involved.