Have one in the appt where I moved at the start of the year, tried it, but I can't spend more than 10 minutes on it and loose the feel of my legs
What really somehow works (and looks even more gay) is the big gym ball, brother has to use it, to fix his back and it really somehow forces you to sit the right way.
As for me the back pain is only a matter of exercise, if I exercise regularly (meaning the gym and stretching yourself time from time), there's no back pain, if I don't exercise it gets painful.