Most important for me: How effective is it as a buffer between me and a vicious dog?
I have never had to smack a dog with one but they do come in handy as a buffer between me and their snarling jaws.
IMO: Diad III was my weapon of choice...had a handle, some size and weight. Diad IV still works for defense, but my hand is almost too close for comfort.
The clip-board looked big to a dog and would keep most at bay. Or you could use rolled up delivery records if it were a full pad.
Diad V looks like an expensive crunchy chew toy..