The kettlebell was not popular in the US until about the mid-2000s or so. Pavel Tsatsouline is credited with introducing the kettlebell to the US from Russia. I'm glad he did.
There are three distinct advantages to using the kettlebell for training:
1) They are SIMPLE. You only need 2-3 for a great workout.
2) They allow for training POWER. The integration of power movements into a workouts is easy with a kettlebell.
3) They're FUN! The complexity, challenge, and novelty of many kettlebell exercises makes it a blast to use.
The disadvantages & limitations of using kettlebells are as follows:
1) The likelihood of poor form and possible injury is relatively high.
2) For maximal hypertrophy they will never be QUITE as good as traditional free weights or dumbbells because grip strength will limit maximal overload for most people.
1) Always warm up and stretch first.
2) Start light. 5-10 pound kettle-bell for women. 15-20 pound kettle-bell for men.
3) Study correct technique and have a professional check your form before increasing weight.
4) Keep it simple. Master a few basic exercises like the swing, and clean and jerk, before moving on to more complex exercises.
5) Use kettlebells primarily as a means to build power, grip strength, and total body coordinative strength. Use free weights for hypertrophy and / or power, and floor exercises / bodyweight training for stability and flexibility.
I saw my brother this past weekend, who I had given a kettlebell for Christmas. I noticed immediately after only 4 weeks his posture was better and his shoulders were more toned and developed.
If you've never tried the kettlebell, I suggest you give it a shot!