Kettlebells are an overall body device in a way that a lot of other weights are not. I learnt a lot from dumbbells but their impact was limited to my shoulder girdle and arms. Kettlebells impact all over / up and down. See demo:
http://kickbike.blogspot.com/2008/12/kettle-bells.html
However, every time you up your exertion level or weight you are going to pay for it so take care and always swing them bless correctly. I do em in the gym and at home. Great domestic gym equipment in one bell -- and one bell is all you need: 8kgm or 12kgm or 16kgm