" … This means students can automatically see what a textbook costs on competitor sites like Amazon and Chegg before being forced into paying the full list price. The extension’s price-comparison engine even displays a range of editions, including new, rental and used, saving students an average of 70 percent off the bookstore cost." …
http://www.businessinsider.com/textbooks-just-got-a-lot-cheaper-thanks-to-2-college-grads-2015-1