REA books are NOT strong for test prep. They do a good job with their academic course reviews (Biology, Chemistry, etc.) However, their simulated test questions NEVER look, taste or smell enough like the real thing.

While I've never played with the simulated CAT on their CD, I am disinclined to trust it. Since their GMAT book has tons of questions that are really not test-like, it's, it's hard to imagine that they've done the due diligence to develop a CAT that FEELS like a simulated GMAC test.

If you already have the REA book, you can use it for your early content review, but I absolutely wouldn't trust it to inform your understanding of what the exam is really like.

As for their test's ability to give you a meaningful score, I would be careful to not rely on their scoring.

If you've already taken an REA practice test, take their number with a grain of salt. If you got a high score from REA, great: use that experience to build confidence when you move on to the more reliable simulated material (Kap, TPR & GMAC). If you took REA's CAT exam and did poorly, don't despair: their software is a blunt tool.