Due to their childish spat with Google, Amazon still actively blocks Google Play Movies from being installed on any of their products. All of my movies I buy and redeem the digital copy for are on Google Play movies so if you're like me, you're out of luck. There are ways to hack it on apparently, but I don't have the time or energy to spend that time researching something that Amazon won't allow because they're having a temper tantrum over Google.
Also, to get 4K streaming content, I have to use the 5 Ghz bandwidth on my wireless router - but my Ring Doorbell will only work at 2.4 Ghz - and they won't talk to each other.
Not impressed - I'm going to go look at the new Google Chromecast with Google TV - they actually let you install Amazon Prime Video on THEIR products.