I took the last SAT (out of 2400) in December 2015. I need to take the PSAT this October and the SAT in December-May…
What are some good prep books/courses for the new SAT?
In the past I have used the College Board Blue Book, 2400 expert (now prep expert), and Reason Prep.
Are the test in the blue book of similar difficulty to the actual SAT?
There’s one official College Board prep book for the new SAT. It has 4 sample tests. You can also download these tests off the internet but by the time you pay for paper and ink, you might as well buy the book. Best price was on Amazon.
My daughter used it, her practice tests fell within a 100 point range and her result on the actual test was within that range.
The practice/placement tests are available on Khan Academy through their partnership with collegeboard. I’ve found this to be the best way for me to study since they also have a ton of smaller diagnostics and practice problems built in. I’ve liked this because it’s been easy to pinpoint the type of problems that I tend to have trouble with, and then learn to do them correctly. I’m not sure if it’s all the same information that’s already in the books, but the online format and (no) cost have really worked for me 
The practice tests in Barron’s New SAT were helpful for my son.
^ I haven’t used Barron’s for the SAT 1, but I did use it for both the Chem and Math 2 subject tests, and they were extremely helpful. I wouldn’t be surprised if they were just as good for the regular SAT.