I got these shoes in black 4 days ago, and I've worn them every day since! I don't think I've ever been this satisfied with a pair of shoes!
There was no breaking in (they hurt the back of my heel where the shoe hits on top for an hour and that's it) and they dress up any casual outfit perfectly! The padding on the ball of the foot is perfect. I've gotten compliments on them already, and I know I will wear them at least twice a week as long as they last, because they are the perfect black flats.
I don't think you will find other flats that are this classy and dressy, and yet this comfortable. They are very bendy; which adds to the comfort and ease of breaking into them.
As far as sizing goes, I bought my usual size 9, and they do come off my heel a little (it's impossible to run in them because they fall off), but if I put a finger in the back, my toes squeeze in the front. I say buy your usual size, and if you're in between sizes, go smaller.
My only small disappoint is the rhinestones aren't as shiny as I wish, but that is also an advantage because it makes them more versatile.