you need to look at it like this, cliffs is an abridged textbook, meaning it was written to teach. concepts are approached like the would be in an AP class. Feralis is essentially someones notes. They aren't really structured to teach, as much as to convey information. granted the info is important, but it comes down to just memorizing someone elses notes.
I used a combination of both. When i need to research a topic more in depth, id open cliffs, and when i was just trying to go over as much previously studied information as possible id use feralis.
That combined with destroyer helped me get a 24.
Hope that helps