I've been sitting on a plain ball for some time, but found that in the summer, the latex is too hot, and you tend to sweat in places that can be uncomfortable. I tried to put a towel over the ball, but then it was too slick to stay on.
I saw this, and figured that since the legs adjust, this might be ideal. The ball won't move as much, so I could use a towel as padding to give me a layer between myself and the ball latex. This part of the plan worked! It's much more comfortable now.
However, the wheels on the chair are not very good. I will have to call the vendor soon and ask for some replacements already, (a couple of the wheels don't swivel very well, so the chair is very "jerky" when you try to scoot in it). Also, be careful to adjust it first, as if you have it too high and try to sit in it, it will shoot out from under you with an amazing velocity.
Note also the wheel locks are very easily accidentally set by hitting them with your feet. The wheels and wheel locks on this chair are actually not well designed or thought out.
After several weeks of using the chair, the wheels got worse. Also, if you bend over to pick something up off the floor while sitting on this, the chair can/will shoot out from underneath you and splat against the wall. This amuzed my co-workers, but didn't do my dignity any favors. Get the other model of this chair and save yourself some grief. I no longer use this chair.