None of the devices mentioned in the OP have had any kind of mass hardware failures AFAIK. Any electronic device will have some percentage of failure of course, but I don't recall there being any model of Kindle, Kobo, Nook or Onyx having any kind of large number of failures. Of course the weak point on any eInk device is the screen and it's thin glass substrate which must be treated with a degree of care since it's somewhat fragile, but even the screen isn't that fragile.
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