I bought the flat sheet with the sewn in corners because I was tired of having my top sheet come off my bed every night. The concept is very good. I like that you never have to worry about making each side even as the fitted corners take that guesswork away. The sheet has however been pulled off at night. There’s not much that gets tucked under the mattress, only a few inches. Perhaps if they made this part longer so the weight of the mattress could help anchor it that would make it better.