I have the book you mentioned - I'm still learning myself but I haven't found any glaring errors in the book so far. I haven't tried rewiring a motor from their instructions yet though, so I can't speak for that section.
I actually lent (semi-permanently) to a friend who inherited her grandmother's Featherweight and has been too afraid of it to do much in the way of cleaning it up and getting it ready to be used again. Since they use a FW for a lot of the photos in the book it's been easy for her to follow.