So, from far away, I think it looks pretty cool. But up close, I hate almost every single one not only due to poor fitment, but becuase the design itself doesn't look good. The fact is the, duck was a quick engineering fix, and the form is the result of compromises- the biggest one being it's method of construction. The factory ducks, and almost all the repops, sit proud of the factory decklid, and produce a bumped out surface under the duck.
I had a whole thread on it here:
http://forums.pelicanparts.com/porsche-911-technical-forum/1130110-ducktail-critique-industrial-design-perspective.html
From a design perspective they all look wrong/****ed up to me. YMMV, everyone has an opinion, but the way the surfaces are formed all wonky would drive me crazy every time I looked at it.