I’ve used one for years. Originally the Waterpik, which broke after a few years, I then replaced it with another, which only lasted for a few months. So I then got a “knock-off” at about half the price, which is still going, although the on-off switch sticks sometimes.
I think the larger models which plug into the shaver socket are more powerful, as the rechargeable ones have a rather large handset to accommodate the tank, and can be a bit awkward to hold.
They are excellent at removing food debris from between the teeth, but I don’t think they remove the sticky plaque that forms on the teeth, for which you need to use the TeePee brushes.
As already mentioned, you must use warm water, and the knack of closing your lips over the nozzle to prevent getting soaked! And start on a low setting, gradually increasing the setting until you can tolerate a higher setting.