I think the book is good to nail down the concepts and equations.
But, I would definitely do some more practice tests in the passage format.
I am using some Kaplan subject tests because I hear that Kaplan has tough PS material. I hear EK is pretty good as well.
I have tried to look at all the sources I can get and make the best choice I can based on what I think will help me the most. One can only do some much practice material. Pick what you think is the best material for you and go with it. It all else fails, you can always take the test again.