The ducktail is a little difficult to see in the middle of that Erector Set on the back of the FD with the Pantera Ducktail.
I think the part is very well thought out. It is a replacement for the original center section, so it mounts positively (no tape or drilling) and looks fairly stock. Its not really a ducktail spoiler the way the term is used in that it doesn't have a lip to it that catches the airflow and pushes the rear end down. It probably has no measurable aerodynamic impact at all, though it could add 1 mph from being a bit more slippery.
I just took my Spirit R wing off my car and its naked right now, but I'm designing my own duck tail spoiler for it. But, if my design doesn't work or look right, I should probably get one of these and see what I think of it. (Hopefully, if I end up staying naked, somebody here will want a slightly used wing for less than retail.)