re: Crosscut Sled with Replaceable Slide-in Inserts (Tools Free)

Another well-designed project with so many useful features.  I have only used MDF on a few shop projects.  Curious on its use versus plywood.  For flatness and stability?  Does the finish and wax "seal" the edges of the MDF?  I still have some of the MDF from an old project, but just haven't put it to use (maybe the mess when cutting impacts my decision).