I have one of these. The good news is that you can install Kodi and I can confirm UHD support. However, it does not really support Dolby Atmos.
And for some ridiculous reason (although this is Fire “TV” and not a “stick”) , 4k Fire sticks/w remote are only $24.99 BRAND NEW at Best Buy, while here at WOOT (owned by Amazon) and over at Amazon, they are much more expensive. 
These are available on Amazon right now for the same price brand new. . . no refurb.
Hmmmm, I see unavailable.
https://www.amazon.com/Amazon-Fire-TV-Streaming-Media-Player/dp/B00U3FPN4U