One reason I like using kettlebells for my training (and clients') is the versatility they offer. I feel they are a nice complement to barbell training. They allow you to perform additional movements that help you develop movement efficiency. Movement efficiency is a term used to describe how well you move your body or how well you move objects. It is a combination of your anatomy, joint flexibility, joint stability, strength, balance, muscular control, and coordination. I feel, it is the foundation for all fitness and sport training.
The kettlebell windmill is a good test of your movement efficiency. Most people are not able to perform this movement with much weight or range of motion. They lack shoulder and hip mobility, and torso and shoulder stability. Often, they will move too much through their lumbar spine and can immediately feel stress/pain there. This is a red flag and they must take a step back to address their limitations.
Below, I perform the kettlebell side press-windmill with my right arm with 24kg/53lbs. This is one of my favorite exercises. I know if I can perform it with ease, then I know I will tolerate other movements (running, basketball, or weightlifting) well.
Kettlebell Side Press-Windmill from Dan Hubbard on Vimeo.