Difference between Kindle and hard copy study guide for CLEP exams

[BeSmart01]

I've primarily used the kindle version for CLEP study guides, but I recently used a hard cover study guide for CLEP Social Sciences.  The Social Sciences book was (I thought) longer, and it had study guide questions.  It seemed to have more content than the Kindle books I used.  Should I use the hard copies, or is there no difference?