If you are thinking about getting a set of dumbbells, think about this. Why are you considering getting dumbbells? Are you going to use them to exercise muscles in your body, or use them as a doorstop? Of course the choice is yours, but consider this. Wouldn’t you be better off buying something that simply works better and faster?
Kettlebells were created in Russia as a cast iron weight that look something like a cannonball with handles. More modern design keep the original concept but most sculpt the weight to give a little more sophisticated look. Some manufactures will add a rubber or rubber like coating or covering to the kettlebell to improve safety for floors and anything else they may hit.
Kettlebells simply work differently from barbells because the center of mass, or the weight, is extended beyond the hand and supported under the handle as opposed to inline with the handle as they are with dumbbells. This allows for swing movements not possible with traditional dumbbells. Because more muscle groups are utilized in the swinging and movement of a kettlebell than during the lifting of dumbbells, a kettlebell workout is said to be more effective, and yields better results in less time.
This is because the center of mass on a kettlebell "swings", so micro-muscles in your body are needed to help balance it , thus utilizing much more muscle activity than a dumbbell. The existence of a handle allows for "release moves" which are simply not available to a dumbbell. This is kind of like when you perform new exercises or participate in events that you don’t normally do, you notice the next day that you have muscles 'hurting' in some areas of your body where you didn’t even know you had muscles. As so the saying goes… This is because you are using muscles you don’t normally use.
Although dumbbells and barbells are good if you don’t have anything else, kettlebells simply provide a better workout because they use more muscles just to control the weight. Add this to the act of lifting, and you have more muscles involved in your workout. Thus you get a better and more natural workout. Any exercises with kettlebells simply utilize the entire body - legs, butt, abs and arms.
Oh, and, if your answer to the first question was to use the dumbbell as a doorstop, the kettlebell works better than a dumbbell for that as well.