1) It's fairly easy to make--easy structurally.
2) Since the front and back boards are covered separately, you can use up smaller scraps of decorative paper.
3) The long stitch binding is hidden by the bookcloth covering the spine. That makes for a very neat, clean package.
4) It's sturdy, neat, and looks really good.
Basically, you just cover your front and back boards with the cover paper and paste the leather/bookcloth spine piece in place between the covers. In this case, I chose an Asian-feel paper of black and metallic gold fish on bright red paper. I used a piece of black silk bookcloth with both a sheen to it and a slight slub.
Cut a second strip of the bookcloth and sew the signatures of the book to it. I used a simple butterfly stitch. Then lay the book block in place inside the cover, glue down the "hinge" made by the inside bookcloth, then paste the end papers in place, covering over the "hinge"
Put it under weight for a while and you have a very nice, sturdy little pocket or purse book.