In the past few years, we have covered plenty of fitness trainers that use water to add instability to your workouts and push your body harder. The Nucleus Core Pro is also worth a look. It comes with non-slip rubber handles and uses a liquid blend inside to generate resistance as you exercise with it.
As you move Nucleus in one direction, the liquid goes in the other direction to create adaptive resistance to activate your muscles. It is useful for core, strength, endurance, and flexibility training.