Cliff's book is in my view hard, in a sense that there are few things specially in Chemistry that you cannot understand or do in a time limited situations.
Biology is okay, math can get tough at times but even then its fine.
Vocab and other English stuffs, you can practice those things using online tests that u can find for free. Ask Google for that!
Bottom line, I think personally, it's a good book to practice your PCAT exam and also to refresh few things that u might have forgotten.
So, go get it!!! Hurray!!