I bought this book among many choices because it had real people demonstrating the sexual positions and that the printed version had 640 pages in color.
After purchasing, I discovered that even slight changes in position were given different names, so meaningful positions are much fewer. In practice, it would be hard to remember these positions when the difference is so little.
If you are buying the Kindle version, be aware that many of the pictures and related texts are NOT on the same page, making learning to try each position much less convenient, as you have to page back and forth to try to understand the text and the picture.
Furthermore, in the last section of the printed book, there are "checklists" of positions - small pictures of 5 X 5 = 25 positions/pictures per page (7 pages total) that can help the reader to quickly choose ones to try. In the Kindle edition, you don't get this 5 X 5 grid, you get one small picture per page, leaving a large area of space. Using this presentation, this checklist is no longer helpful, as you must swipe hundreds of times to go through the choices.
I later bought a Kindle book (The Guide To Sex Positions) that costs less than 1/3 as much, does not have meaningless slight variations in sex positions, and has both picture and text on the same page. The organization is also better, as you can find positions in alphabetical order or by type: 69, Cunnilingus, Fellatio, Butterfly, Cowgirl, Exotic, Face-To-Face, and Rear Entry. The presentation is not done by real humans but is instead computer illustrated. Although the graphics size is also small (to accommodate both picture and text on the same page), it is very understandable.