I have the Mini - it is a wonderful device.
Very portable ... and light!
I use the Kindle app on both my iPhone 4S and the Mini to sync my books. The cool part is that you can take books that you did NOT purchase from Amazon and send them to your personal documents up in Amazon's cloud. Then, you can sync them between devices with Whispersync. I sync almost daily between my iPhone and my Kindle - so I know it works a treat.
See this link for more details on Amazon's Personal Documents feature:
https://www.mobileread.com/forums/sho...d.php?t=163465
Marilyn