I purchased the red neon powerball as it's £2 cheaper than the other neon balls, not that looks matter. Its what it does that makes it awesome.
Great for relaxing, exercising etc. you won't want to put it down, even when it feels like your arms are going to fall off!
If your thinking about buying one, stop thinking and just buy it :D
I wouldn't bother with any of the accessories that you can purchase separately. For example the auto starter....complete waste of money, the powerball is all you need.