I have both books and they are both worth having though I did lend my OBW book to my mom, she wants to try after being here playing with mine.
OBW is a type of S & W. They have the same block in the S&W book. The one block wonder uses the octagon or the hexagon, and have you do the whole quilt out of one fabric.
S&W has several different blocks in several different arrangements and to do the main pieces you use the one fabric, but they incorperate other things into it as well, it has the fan and a square as well as the hexagon and octagon, cut in the stack fashion.
Kalidescopes are done on the same sort of fashion, but are fussy cut to get certain aspects of the design of the fabric.
Both ways of laying out the fabric is easy. It is a personal choice.