I took one on our trip - just got back today <sniff, sniff>.
I didn't have any trouble at all with it and security. Even the TSA didn't question me. Only once entering the MK, my dh was carrying it for me, because of course I'm the momma pack mule with the tickets, water bottles and everything else, was there a comment about it. The cm when we entered, a young foreign girl (I won't say her nationality as it is immaterial) told dh "use as cane, no seat!". I said to him afterwards that it's a good thing I wasn't carrying it, because I would have told her that I spoke with someone in special services who said it would be fine. Had I done that, it just would have complicated the situation, so it was better I didn't know until after the fact.
I got so many compliments on it! Everywhere I went, people said what a great idea it was. It was a god-send on long waits for busses and rides.
Dh thinks I should write to Dick's and ask for a portion of their profits on them in the future since I was such a good advertisement for them. I think I should figure out how to make them with a mickey head on the seat and sell them on ebay!