I am on the bottom end of the sizing range so mine is not too small.  It is appropriately snug so I could see where someone would consider going up a size if they were on the top end of range.  

Takes a little getting used to for a first time monofinner but after a few sessions, you feel like your flying through the water.  My labrador retrievers can't keep in the open water!  Sometimes I get to going so fast, my goggles come off and my ear buds come out (Nu Dolphin - also highly recommended).  

Such a great core workout.  If your ankles are weak like mine (too many sprains in the past playing basketball), then you might want to ease into it with alternating sessions with and without the monofin.