OK, I can confirm that right now, getting Amazon Prime (US) is doable with Getflix. I havent signed up though, and I have switched to the Aus store for books… Not sure how Getflix might make changes to the subscription, or if once subscribed I would get pushed back to the AU store. Here it is, working.
On previous attempts without having the Getflix DNS set, all I could get was that this was unavailable in my location.
 And signing up requires that I either change my country for Amazon, or content myself with Australian content, in which case GEtflix is not required.