I bought a Fairywill one off Amazon. It stopped working after about 6 months, but they were really good, replacing it with no trouble. The second one has lasted 18 months so far.
I'm amazed that, even after cleaning my teeth, it still gets lots of little bits out of the gaps between the teeth. I first bought it because I was getting toothache in a back tooth. The dentist was going to take the tooth out, but I persuaded her to give me antibiotics and I bought the water pic to keep the gap scrupulously clean. It's worked for the past two years!