Sit upon
I bought 2 of these a cpl. of yrs. ago when we talked about them & pd. more than this for them. I find them to be miserable. Those little nubbies seem to hurt my bottom. They aren't big enough for my bottom either which doesn't help. Yikes, I can't believe I told you I have a big bottom. LOL. At least broader than 13".
My 6 yr. old g-dtr. loves using one as a booster at my dinner table so it wasn't a complete loss.