Different from hand weights. The key is using your core to swing the bell, not your arms. We do a lot of KB swings in Crossfit and we never swing to the side; always vertical. We also do squats with them and occasionally box jumps. It is an amazing tool; I definitely have a love/hate relationship with it. I think the one I'm currently swinging is 35 pounds. I started with an 18 pounder (I think). In addition to Zen's link, you can read more about it on this page .

If you have an opportunity to try one, give it a whirl. I wouldn't buy one without trying it.