I had a go on one of those machines the day of my wedding!
I asked my mum to book me in for a seaweed wrap and I got that instead!
Its not so bad, a bit weird, you're tummy does feel like its being squished around a lot but you get used to it. If you've ever had electrolysis, given birth or had a tattoo then I wouldn't worry this will be a breeze.
I lost an inch during my session, can't remember how long it was, but can't say I noticed any change, I was mesured before and after. Its more of a quick fix, definitely not a long term thing. Go for it, can't do you any harm.