To be honest, I'm more impressed with these smaller, condensed versions of the Logo Lounge series. While their larger counterparts do include more material, (specifically case studies) the quality and amount of that material really doesn't justify the price. (The hard cover versions of these books are $50. I wouldn't pay more than $39 for it.)
These condensed editions show only the logos themselves, which serve as a terrific quick reference for ideas. And at $19.99, they're certainly worth adding to the design library.