A friend was joking (I think) about buying this exercise ball chair, the Sitness 5 by Topstar, from Overstock.com. Now, I can see the appeal of wanting to sit on something at work that looks like a chair rather than an exercise ball. But the truth is, when I’m sitting, I just want to sit — no exercise ball or Hawaii Chair for me. Anyone use something similar to this at work? –Mary T.