The tree of the knowledge of good and bad gave them exactly that: knowledge of good and bad. They suddenly saw that they were naked for example. Soley a testing tree or "carrot" could have been a simple apple tree. But this tree actually did something, and is very telling as to the innocence of Adam and Eve prior to eating of it.
I don't think they gained the knowledge of good and bad at all when they ate from the tree.
In this story, God said that it was 'Good' after He made the 'naked' humans. They were 'good' , but when they ate, they saw their nakedness as bad. To me, that indicates their 'eyes' were closed, rather than opened. They couldn't tell the difference between good and bad anymore.
I think when they ate they got confused rather than enlightened in any way.