I wear a 12 1/2 shoe and ordered the 12-13 size (EU 46).  The fit for me is just right, but I have wide feet.
These are initial impressions and might change, but very comfortable right out of the box.  Enough room to slide on easily, but they stay on while walking.  Some initial odor, but the included tag indicates that the smell will go away after a couple wearings.
Update after a few weeks:  still 5 stars and since it's summer, the only thing I wear on my feet most of the time.  Shoes come off and these go on as soon as possible.  Just enough arch support, just enough strap area, just enough heel cup.