Essentially the Glützhauw or Clashing Cut is a Zwerch. But instead of striking with the edge on edge, you hit his blade more with your flat. You then ride his edge down his blade until your short-edge makes contact with the side of his head.

Higgin’s Armory has a demonstration of this. Make sure you note the text, as the fencer on the left intentionally missed for safety and theatrical reasons.

http://www.higginssword.org/guild/demo/interpretation/clasher.html

Another way of looking at it a Zwerch is a stesso tempo (single time) action while a clashing cut is a dui tempi (two time) action. As such, I see the clashing cut not something I would intend to use so much as something I may happen to use. More of a “oh look, my Zwerch didn’t land but you’re open for a Glützhauw”.