I purchased this for my daughter going into 4th grade. We have done SOTW, but dd isn't ready for Vol. 4, so we will be studying the Presidents and US Geography instead. The two additional resources suggested are excellent. They are the Scholastic Encyclopedia of the Presidents and Their Times, and Have Fun with the Presidents. The other books that are suggested, I find optional. Some are available through our public library, and others I don't feel are worth searching out. The American Presidents by Marilyn Barr is out of print, geared for early elementary students, and useful if you are really into crafty projects. I would say How to Be President is also a marginal purchase. As far as this unit study itself goes, the schedule is nice, so you don't have to think about how to break it down. I also really like the quotes in the Appendix for each President, which I plan on using for copywork. I will be supplementing with other books, worksheets, and activities I've found elsewhere, but this resource is a great springboard.
[5 of 5 Stars!]