What you should know about Kindle Unlimited

The new book-borrowing service Amazon (AMZN) announced last week, Kindle Unlimited, is a close cousin to Amazon Prime Music. Both posit the question, "Why buy content when you can pay one price to consume as much as you want?"

Before answering that question, the basics. Kindle Unlimited makes a vast swath of Amazon's digital book library, about 600,000 titles in all, available for unlimited browsing for $10 a month. That means you can read as many (or as few) books as you like and you pay one price for the privilege. You don't get to keep the books, of course, so if you end your subscription, you lose access to anything you've "borrowed."

This approach, while potentially attractive to readers, isn't especially innovative. A number of ebook subscription services have been operational for some time. Oyster, for example, boasts a catalog of 500,000 books for $10 a month, while Scribd offers access to 400,000 titles for a monthly charge of $9. And Entitle, which operates a little differently, charges $10 a month but lets you download and keep two books each month from a selection of 200,000 titles.

In principle, Amazon's new plan gives readers more flexibility, enabling them to read as much as they like for a single low price. And for some people, it likely is a good deal. You can use the open-ended subscription of Kindle Unlimited to "graze," browsing books until you find a book that really grabs your attention. There's no cost or penalty for reading a chapter or two and moving on to another title.

But service also has limitations, which you should consider before committing to a subscription. First and foremost, it's worth noting that books are an inherently different medium than music. While it's possible to truly take advantage of a vast library of music using a flat subscription, most people don't complete an entire book in even an entire month; you have to be quite a voracious reader to read enough books for the $10 fee to be a smarter investment than buying a book outright for its listed cover price.

Even if you do read enough to take advantage of Kindle Unlimited, be aware that you don't get to choose any book in Amazon's vast library. Five major publishers -- Simon & Schuster, HarperCollins, Hachette, MacMillan and Penguin -- have all opted out of the plan. That means you won't be reading much Steven King or Dan Brown on Kindle Unlimited, nor can you read Brad Thor's "Act of War," the book currently sitting atop the New York Times bestseller list.

Oyster, Entitle, and Scribd all offer books from Simon & Schuster and HarperCollins, meaning they might be better options for some readers. Amazon's advantage, though, is a far more comprehensive array of supported platforms, including their own Kindle devices, iOS, Android and Windows Phone. Oyster and Scribd are more limited. Thankfully, if you're interested in an ebook subscription, you can try any of the services for free for 30 days.