I bought a pair in November 2008 and still train and compete in mine. I bought them from a company in Winnipeg Manitoba.
Although I've squatted off and on in chucks, I return to my O-shoes because they have a significantly different feel to them.
The width of the sole and the hard structure prevents lateral movement of my foot. It feels like a much more solid base and my feet feel nailed to the floor.
The heel contributes to my set up benching as well. Because IPF states that your feet must be flat on the floor, when you have a heel, you can pull your feet back a bit further while keeping the heel in contact with the floor without hyper flexing your ankles. For me, the further back my feet go, the higher my arch goes.