I think it depends on the kind. If they are the plastic/rubbery kind that are absolutely basic for flip flops; you can feel the connecting ends under the soles. You also feel every rock or pebble that you step on.
I don't usually buy those kinds because I have bad ankles anyways and shouldn't even wear flip flops, but I hate shoes in the summer. I usally buy the thicker soled, leather strap across the feet type. I also usually buy them in the mens section. I would rather pay a little extra for a pair that sole and straps will hold up a little longer than a pair that are not comfortable to start with.