Waterpic washes out debris from gumline and between teeth that is missed by brushing alone. More convenient than flossing and teeth feel cleaner after as well.
I have a partial, and it cleans out that area that near impossible to do before. It also gets everything out from between my tight teeth spacing very well. Love it!
It's a bit bulky in the hand and you'll have to either switch hands or rotate the WP-450 to get the inside and outside of your teeth. However it does a great job and is less of a counter clutterer than te tank unit.