So.. I got sucked in by the hype and coughed up 20 quid for a neon blue powerball (for those who don't know what they are: http://www.powerballs.com/). I've been mucking around with it for about an hour now and i love it!
Time will tell if it actually builds up my muscles, but it's definitely a strain on the arms If not, well it's still a lot of fun!