Joe, Surprisingly, The plastic shoes actually last as long or longer than the steel shoes. They are usually made from the same stuff as Skate Board Wheels. They seems to tolerate the abrasions that wear the steels shoes into knife edges.
My concern with the plastic shoes has been that they still flex slightly, Which is why folks like them. But that flexing allows the nails ( if nailed on) to flex and move, which enlarges the nail hole in the hoof wall. Maybe glueing along with nailing would solve this problem. Something I would have to explore more if I were to try to use plastic shoes.