I have a 3x5 and two larger ones (4x6, I think?), and they’re great. Wash well and the edges don’t curl. Two are are in the entryway and I have a 60 pound dog that uses them as a launch pad, and they stay remarkably flat. I do have a round one under my kitchen table that is harder to place and the edges tend to curl if it’s not placed perfectly.
I think it really does depend on size, and perhaps they even vary by color?