I tried this chair for about 3 hours. The next day I could hardly walk. Both of my hips hurt so bad. I am going to try it again a little more each day and work into it gradually. There was nothing mentioned in the brochure about having to work into it gradually.
I brought this Classic Balance Ball Chair a month ago and am so glad that I did. It's comfortable and supports my back while I am on the computer. I am 5'3, 130lbs and the height is perfect for me. It's not too low and it's sturdy.
I've been using this chair daily at my desk now for 2 weeks and I LOVE it! It has provided much relief for my back. It makes me very conscious of how I am sitting. Did I mention that I love it! :-)