[jbcohen]

I don't recommend that the secondary hardware be the same model as the one that its a secondary for. As computer hardware ages they get less dependable and more prone to breaking down, hence I recommend a Kindle Paper white paired with a second generation kindle or a first generation one. Its not a good idea to backup a kindle three with a kindle three, they are older hardware and equally unreliable.

I might at some point backup my kindle three with a nook. Since they are different ages and different brands they are a good backups for each other, however I the nook costs too much at this point.