None of the eBook readers is really limited to one vendor, nor are eBooks from a given vendor available only on that vendor's eReader. Conversion is simple enough with Calibre or other software, and DRM can be removed if you push the limits of ethics a bit for your own use. There are very few books available (for example) for non-Kindle readers that are not available on Amazon. An alternate option is to use the computer reader software on a computer to buy and read a DRM-enabled book from another vendor that doesn't work on another reader. Content has become less a factor than the media functionality.
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