MDF makes a fine top for a router table or a workbench, or just plain old jigs. It does need to have a finish that protects it from moisture. I use Watco oil, plain or colored, makes no difference. Let it dry thoroughly, add a coating of paste wax like Johnson's, and you will have an excellent top. An occasional waxing will keep it slick. Johnson's is also good to protect your cast iron saw tops, etc., and things will slide better also. Just remember to buff out the wax.
Regards, and Happy New Year to all,