There are plenty of folks who have a Nook or Sony for library books and a Kindle for other reading. There will be files that are easier to load on the Sony, a non-drmed Epub, then the Kindle. Then again, Amazon's store is larger then Sony's and it might be that bainsy enjoys buying through the Amazon store.
If you think you can afford both and will benefit from both go for it. Take a look at the books you can get for the Kindle at Amazon's website and other websites.
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