Ive had an Asus Transformer with the klip on Keyboard for about a year now and its great with the keyboard on its a mini laptop and has a massive battery or take the screen off for a tablet
the tablet prioritises the 2 batteries to conserve the screen one so when docked it uses the keyboard one first and or charges the screen one I can charge the keyboard separately and carry on with the screen ie to read in bed while the keyboard charges for the morning (they claim 16 hrs from both batteries on video but as usual its not accurate but its still a pretty long battery life compared to others)
can take a SD card and 2 USB sockets in the keyboard and a micro SD in the Screen part so can add extra storage (lots off) and transfer files easily from cameras etc or have a Music Card and swap out for a photo or files one
Ipads you have nothing so easy
Wife has a Ipad and Iphone
I have android phone and tablet to me much better designed for the user not apples convenience
Kindle app is loaded on it anyway
BUT the last upgrade they locked out any books not bought from the kindle store which is a PITA as i have loads that aren't from there so had to load another reader half way thro a book)
pretty much any app on Apple is available for android