After reading the reviews I wasn't sure how I would like the chair. I LOVE it!. Yes, the base is made of a molded plastic but that isn't a bad thing. It makes the chair easy to move around. I also read that the chair is short. That is not the case if you fully inflate the ball. I am 5'5" and I had to actually let some air out as it was too tall for me. It also keeps me from slouching. My main goal was to strengthen my core and it is doing just that.
I bought this for my office at work. Very easy to assemble. Lightweight so easy to carry and transport. I'm 5'4 and I was able to inflate the ball to correct height. The first week, I could feel my muscles in my back adjusting to my new seat. But after then, been very comfortable.
I love my chair; however, I have cats and one of them scratched the ball. Not enough to go all the way through but enough to make it leak air. So order a cover for the ball if you have cats. Yes, there are covers for the ball.
I like the back addition so I can put a pillow back there for comfort, mostly I sit without the pillow but when I work a lot a pillow helps. I find myself bouncing and it keeps me active and working longer. My husband and I both use it at home. Great for those that work at the computer a lot. I bought one for my daughter for the holiday.