Get the $79 model. The ads aren't intrusive at all. They only show up as screensavers and a small panel at the bottom of the home page. The ads never appear inside a book.
I went from the K3 with Special Offers to the K4 with ads. I was happy to ditch the keyboard. I considered it unnecessary bulk and definitely prefer the smaller size and weight of the K4.
If you have an Amazon Rewards Visa, you can get the K4 for 40% off; making it a bit over $47. If you don't have the card and qualify for one, you'll get an instant $50 gift card; making the K4 free.
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