Need to return these, I ordered per my shoe size (10 mens) and they are much too large and don't fit right.  The rubber strap across the bottom is too thick / large and my trail shoes aren't designed with a recess that allows the bottom strap to fit.  They probably fit Salomon shoes better (I run Saucony).  I would try a medium if I thought they were worth it.  Ran a 13.5 Spartan Beast without them and didn't feel I needed them after the event.  I admit gaiters may help with keeping dirt / mud out of shoe, but these aren't for me.