A couple of my friends have gotten them as gag gifts. The commercial makes it looks like they move due to some electronic device and your workout is to stabilize it. Really, it's just a piece of plastic that you jiggle. It's not heavy, and making the motion smooth enough to jiggle it properly is... ridiculous to say the least.

You would be just as well off picking up any one-pound object in your house and shaking your fist in the air.