I use my kindle app on my ipad, works great for me. But I also have a kindle and use that more often if I just want to read. If I use my ipad to read I often end up surfing the web, checking sports scores/this site, or just pissing away my time instead of reading. On the Ipad im too ADD.
My wife says the kindle app is only good for reading, but not for organizing or even buying her books. She uses her old school kindle for that. On the other hand, if you find the app sufficient, then you get the benefit of both iBooks and Amazon with the iPad, where kindle is limited to just Amazon. I prefer a device I can use for other things.
If she is just using it to read, then the Kindle Paperwhite is probably an easy choice. <$150 vs $300+ ($400+ for mini w/ retina) 7.3oz vs 9.6oz weeks of battery vs 10 hours plus less eye strain and easier to read in the sunlight. Of course, if she wants a tablet, the iPad Mini (or some Android tablet) is the way to go.
I just use the kindle app because my father, who has a very similar taste in books and my mom who doesn't, are both big readers and buy a shit-ton of books. So I have their account on two devices (one account can have up to 5 devices). So I usually only buy a couple books a year, the rest I just read my dads books. Right now I'm reading 1491, a book about the Americas before Columbus. Real interesting, our understanding has greatly changed over the past few decades through archaeological digs and data analysis, so what I learned in school is now extremely outdated and in some cases dead wrong. For example in school I remember learning that it was thought that there were a few million Natives before the Columbus, but that number keeps getting adjusted upward every time they find evidence of these giant cities. The best current estimate is now 60mil, but the author believes once the dust settles the final best estimate will be about 80 million Natives in the Americas. I recommend this book if you like nonfiction.
There have been quite a few discoveries where there was once thought to be a tribe or two, but now we have miles of hills that are all made of pottery, so much so that it's evidence of some of the largest cities the pre-industrialized world had ever seen. Mind you, I'm talking about the entirety of the Americas, not just America or North America.
I'm talking the americas, too. The bulk of the population would be Incas and Aztecs in South America. There are no other massively large cities that suggest population of 80M. Seriously, the US had an 80M population in 1900. That means cities like San Francisco, LA, NY, Philly, Chicago, etc. Too big to just be lost in the jungle.
Some were actually purposefully buried. Your estimates go right along with what scholastics believed a few decades ago, but those numbers keep getting revised. The best estimates currently suggest 60M, and it's the authors contention those numbers are still climbing. I just started the book, maybe 50 pages in, I'll report back with more specifics when I learn them. Personally, I have no idea and don't know how to judge, I'm just reporting from the book, which seems quite reputable.
So according to that the best estimate is 40M based primarily on a couple books written in 87 and 98. Considering recent findings have been resulting in an uptick of estimates, I would say the 60M I mentioned seems quite reasonable.
Read the link. The estimates are all over the place and new information does little to form a consensus. Feel free to find links that show a few Chicago sized cities have been found.
In 1492 it is estimated there were over 60,000,000 Buffalo in North America alone, and yet, no massive buffalo cities have ever been discovered.