Very cool to hear some of the history of the fly Byron. I will have to pick up that book. To me the main advantage of the sparkle dun is durability as I have had those CDC fibers break off, especially after a few trouts teeth have tangled with it. And if I am fishing rougher, faster water I will often choose the sparkle dun. But on lower gradient streams, and the spring creeks that I mostly fish I definitely prefer the more subtle shuck that the Duck butt dun provides.

I also tie my X-Caddis with a CDC shuck. The Duck Butt X-Caddis if you will. It works well.