Quick note: the Math Guide is now available through Google Play as an eBook. You can read it on your computer, your iPad, any Android device, etc. It’s cheaper than the physical book, of course, and you don’t have to wait for it to ship to you once you buy it. So that’s cool.
Still, if you go the eBook route, make sure you have a pencil and pad of paper by your side, and make sure you redraw diagrams, mark them up, and write out your calculations. Don’t forget: The SAT still happens on paper.
PS: If you’d like to join the Make Your Own SAT project, there’s no time like the present!