I tried one last year. For $2 transport included, you can't go wrong. They stay on reasonable but beside walking, there is not much else you can do.
The plastic frame is not sturdy. The C-string rests mostly on your upper thighs and and is stabilized by the tail-piece between your cheeks. Now and then you have to pull up the string but it is fun to wear at the beach. After testing one, I ordered five more strings.
The ones I ordered had a roomy pouch. I had to do some sewing to remodel the pouch sligthly.