When I was getting ready to sell my book, NEVER CHEAPER BY THE DOZEN, through the mail last year, I decided on free shipping via media mail. The clerk told me first class shipping was just a mere four cents more. Fine, I told her, for a few pennies more my customers shall get free shipping via first class mail.
As I remember, the USPS treats media mail distinctly differently than first class.
Never regretted this decision, and there have been no reports of damaged books received.
---Brian Powell