Every time I recommend a Kindle to a friend, they hesitate on the purchase page for ages. Should they get 8GB or 32GB? Should they get the Special Offer version with ads, or the ad-free version? A $20 difference is not huge, but compared with the $129 price of the Kindle Paperwhite, it's not small either. So here's my advice, no more hesitation: buy the Kindle with ads, the Special Offer version! Why? Because Amazon quietly put an option to turn off ads in the settings page! Even if you buy the Special Offer version with ads, you can turn them off without hacking or flashing the firmware, and easily remove the ad shown on the screen when the device is off. There is also a nice bonus: from then on, pressing the power button no longer requires swiping right to unlock the screen!
Looking back, the Special Offer version originally existed to lower the price of the Kindle. Amazon wants to sell e-books, not e-readers, but a reader has its own costs. To bring the cost down, Amazon put its own ads into the Kindle. But as the Kindle became a hit, mass production brought costs down, and e-book sales grew. Now the Kindle no longer needs ads to keep its price low. For Amazon, the ads have changed from advertising into so-called Special Offers, which are book recommendations. Starting with a certain version of the Kindle, Amazon simply went along and provided a way to turn Special Offers off.
This method works for all versions of the Kindle, including the All New Kindle, Kindle Paperwhite, and Kindle Oasis.
Start your Kindle, then tap the "..." in the upper right corner to enter the "Settings" page.

Many articles say to turn off ads under "Device Options," but that is the old way. If your Kindle has kept receiving updates, the newer versions have moved it to "Your Account."

Under "Your Accounts," tap "Special Offers" and you're there.

Now you can turn the ads off freely. Just set all three to "Off." Yes, it really is that simple. No hacking at all. They give you the switch openly: turn it on if you want, turn it off if you don't. So why spend an extra $20 on the version with ads? Don't you agree?
