A) It shows that Zoo is developed by a well known name in Joomla templates and extensions. It boasts a superior interface and is fairly intuitive .
B) Although all CCks have complexity and can be hard to master Zoo has extensive documentation. this might seem like a simple thing but unfortunately quite a few CCKs out there for Joomla seem to care little for how users learn how to get what they need out of the extension.
Using Zoo there is very little you can't get your head around to create compellign websites. I just wish it didn't create another layer of content distinct from Jooml'a default content system
There is little sense in trying to use a CCK if yoy can't figure out how to use it