I read many reviews before purchasing these and accepted the advice to size up.  Huge mistake.  I am a 'perfect' size 10, purchased the 11's and am now wearing shoes that are, well, HUGE.  I would have sent them back if I had time before my vacation but I didn't.  I figured; what difference could a size make?  Well let me tell you, they are horrible!  I end up dragging my toe when I walk and my husband and daughter keep stepping on the back of my shoe when I walk (what are they doing so close anyway)
I will be replacing them with my correct size.  A pretty expensive mistake.

I give them 5 stars because the shoe itself is comfortable and stays on my foot without me having to grip my toes like most flips.
I do recommend you get your true size