I have one but only a cheap thing. Mine isn't very sturdy and tends to flop up a little on the bottom when I sit. But if I'm standing up straight my waist looks more defined alright ;)
One of Sweden's most well known stylist/designer type people, camilla Thulin (used to do the stage clothes for Army of Lovers) says that all women should wear dresses, and under dresses we should wear control top tights one size to big, just for a smoother line, and then a waist cinched. So there you go.