What is your question? The advantage of extended choke tubes for shooting clays?
To me, they only make sense for clayshooting where you might need to change out choke tubes quickly. But where I've seen the best use of extended choke tubes is on sporting clays with an O/U. Say you have a close proximity rabbit and a longer shot, true pair. You can have the ability to run a SK & F if you want.
I only use flush chokes for hunting though. Mostly because I dont wanna lose an expensive extended choke, some of my chokes are shiny silver, and I've never seen the need to quickly change choke tubes during a hunt.