I love flat ballerina slippers.  Pros of these: great foot padding, good price, nice material
  Cons:  They run a little small.
I wear a size 10 and bought the xl.  They are ok, but the length seems short.  It would not fit a 10.5 .
Other than the running a little smaller, it is a really nice slipper.  I like the rubber sole, can even get mail from porch.