i go to powerplate classes at Good Vibrations in London, pricey at £150 for 10 lessons - theyre really good and you hurt like hell the next day, after my first 2 classes i had trouble lowering myself onto my seat at work and onto the toilet and i kind of had a funny walk a bit like mick jagger.. they do what they say, ie in around 20mins you can do the same weight resistance workout that would take around 1hour but you also need to do cardio as they dont support that type of workout - but they are a fast way to tone up muscles. but the cheap ones for home are no good ive heard.