The Waterpik Aquarius 660 and Waterpik Aquarius Professional 670 have so many features in common. Attributes such as reservoir size and floss & hydro-pulse modes are present in both models. However, the 660 lacks a Tip Storage Case, which comes with the 670. Otherwise, the differences between the two models are cosmetic.  The Waterpik Aquarius 660 water flosser is available in six colors, while the Waterpik Aquarius Professional water flosser is available in four colors.