Iv had no experience of one but i have heard that
10 mins on one is the same as 1 hr at the gym so they must be good...
sorry but this is marketing spin from the company who make them!!
They don't raise your heart rate or get you sweaty!
Most people just stand on them as they vibrate. It's a nice feeling in your muscles to stretch and relax after a work out. If you do the dynamic exercises on them , then yes, you get a bit of toning.
To lose weight (if that's your aim) you need to do good old fashioned sweaty exercise!!!
I'd spend the £30 towards a gym membership
xxx