Book Recommendation

In surfing amazon.com I was surprised to find there are books on how to become a better correspondence chess player. Has anyone read any of these? Any recommendations for a mid level player like myself? Also, could someone please explain to me why the book ICCF Gold is worth $270.00?!




https://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=correspondence+chess