The SMAI cast iron kettlebell definitely has the upper hand over the regular dumbbell with its unique design similar to that of a cannon ball with a handle attached, making it an effective tool when developing advanced proprioception by performing exercises like the high pull which has the same movement pattern as a power clean or the two handed kettlebell swings similar to that of the deadlift. One way that the kettlebell helps to benefit comes from the speed and power required to keep that bell moving which transfers directly to the lift.
Using the SMAI cast iron kettlebell is also quite a functional way of training that will have you improving your cardiovascular and functional strength capacity. Some of the more popular exercises performed with the kettlebell include push ups combined with renegade rows, high pulls, one or two handed kettlebell swings, bent over rows and the famous Turkish get-up (the Turkish get-up in essence combines a plank, lunge and bridge in one movement). The kettlebell is commonly used in the sport of CrossFit whether to help in working on their form for more complex movements, to work on their fitness for an upcoming competition or in a WOD.
For beginners the 4-6kg size is perfect to start out with, avoid strain or injury and to help perfect the technique before moving up to the heavier sizes but be aware that this type of training has been known to be highly addictive so in no time you will need to get one of every size.