Re: “unlike tablets, Kindle is designed just for reading”
I don't use an iPad, but in recent months I've read through the entirity of Iain M Banks' sci-fi books, the whole "Prelude to Dune" series and just finished Frank Herbert's Dune (with the rest of the series to come) on the Kindle software on my Motorola Moto G without problem.
It takes all of a couple of seconds to switch the phone on from standby and re-open the Kindle app and I charge the phone when I go to bed.
And, of course, I don't have to carry around two devices when I only need one.
PS and it cost £120 and does a lot more than just let me read books...