Competition kettlebells are made of steel and are all the same size regardless of weight for a uniform training experience at all times. The bells are designed for high repetition exercises. If you have used barbells, think about when you train with plates that are all the same size regardless of weight so your form is always the same during Olympic lifts. Competition Kettlebells are the same premise in kettlebell form.
Specifically top-heavy molded with a thicker handle base and a greater percentage of load toward the top of the bell's body. This ensures that the kettlebell does not pull the lifter's arm to the outside when overhead or in the rack (resting at waist level) yielding injury prevention and energy conservation.
Choosing a kettlebell depends on what you are comfortable with based on previous use and budget. This style of kettlebell is ideal for someone who likes the idea of uniform sizing across all weights and easier balance in the top of the kettlebell. This will help the kettlebell move easier compared to bells of the same weight with the weight distributed through out the bell. These are designed for high repetition exercises but are also great for bootcamp type workouts like push ups and dips because of the bigger base on the kettlebell.