I actually did end up getting them, I won't be using them on my Kindle, since it's sold, but if I can find a way to use them otherwise, I will. I haven't tried using them on my Nexus 7. I am under the impression that I can't, although I could easily be wrong.
I passed on this for once reason. I'm selling my Kindle Fire HDX because the Amazon store sucks. The updates are slow, and you don't get access to tons of games that are on Google Play. This would have been an amazing deal otherwise.
Picked up Killzone Shadow Fall just now for my PS4, $28, +2 ship, +2 tax... $32 and out the door! The cheapest used on Amazon is $36, so I feel like I got a pretty good deal. :)