It is pretty comfortable. I sit up straight, use my core muscles much more, switch back and forth between the ball and my chair. When I start feeling myself slouch I just bounce a few times and I correct it. It is like those bouncy balls we had when we were kids (but without the handle). So far it seems to be working. It is hard to say if the frequent changes, breaks, or ball are the main cause. I think all of the above seem to be helping. Fingers crossed – I hope it keeps working.