Is it worth it to get a PSAT study book?

I bought both the Kaplan PSAT study book and the Kaplan SAT book. I've read through a little of both and they seem to contain the same inofrmation, just where one says PSAT the other says SAT. But like I said, I've only read a little bit. Should I return the PSAT book to get a different company PSAT study book or just get a different company SAT book? Is it worth it to use a PSAT study guide at all when you have SAT study guides, or is it just going to be the same information restated?