Amazon.com introduced on July 18 Kindle Unlimited—a new subscription service that allows customers to read as much as they want from more than 600,000 Kindle books, and listen as much as they want to thousands of Audible audiobooks—for $9.99 a month. Amazon is offering a free 30-day trial for the service.

Subscribers also get a complimentary three-month Audible membership, with access to the full selection of Audible titles. Kindle Unlimited is accessible from Kindle devices or with Amazon’s free Kindle reading apps.

“With Kindle Unlimited, you won’t have to think twice before you try a new author or genre—you can just start reading and listening,” said Russ Grandinetti, senior vice president, Kindle. “In addition to offering over 600,000 e-books, Kindle Unlimited is also by far the most cost-effective way to enjoy audiobooks and e-books together. With thousands of Whispersync for Voice-enabled audiobooks to choose from, you can easily switch between reading and listening to a book, allowing the story to continue even when your eyes are busy.”

However, as The Washington Post points out, not every book the reader wants will be available on Kindle Unlimited even if it’s available on Amazon. For instance, the top five New York Times fiction best-sellers were not on the service when The Post tested it.

The Post points out that readers who consume more than one book or audiobook a month may benefit, but otherwise, the price may be higher than what the consumer is actually spending for U.S. average book consumption.