I bought two of these for my family and returned one and would like to return the used one also. First, the water reservoir is very small and it is inconvenient having to refill it 4 - 5 times during use. Second, the water flow is not as strong as I prefer. My family is extremely dental hygiene conscious and visit the dentist twice a year as I suppose most consumers of this product are, so they will definately agree with me on this. Additionally, working the whole module around my teeth over the sink is clumsy and messy.
In conclusion, this Waterpik is generally is a waste of money. I would stick with the original Waterpik countertop model even though it is not portable. The portable aspect is not a great enough benefit of this product to overlook the flaws I have mentioned.