These were recommended to me by a swimming instructor. However, they are cheap and flimsy- they are basically big baloons. And you don't need them- just make a fist in the water for the same effect. The purpose is to get you to pull with your forearm as well as your hand. Don't need a device for that.
These are alot of fun, and really let you feel the stroke in the forearmThese are a great tool to use in drills.