Water picks for your teeth do work as advertised and I use them myself and they do a wonderful job however dentists do not recommend people use them.
Most dentists recommend string flossing, either in addition to or instead doing water flossing but water picks for teeth is okay and I find it works for my teeth.
I'm not sure why dentists do not recommend the water picks because they do work wonderfully and are worth getting and using.
However I would still do string flossing along with the water picks to have even cleaner teeth.