Purchased one yesterday to get access to Itunes 4K content. Picture quality in 4k is surprisingly sharp for streaming. For instance, Netflix UHD looked sharper than my LG C7 inbuilt app.
Main strengths of the device based on my limited usage so far:
A. Great build quality (given its Apple)
B. Dolby Vision (only source for me so far, dont think there are many sources for Dolby vision content currently) - looks absolutely stunning, and yes its better than normal HDR
C. Itunes movie purchase - this is again the cheapest way to own a 4K HDR movie. India prices are around 700, while a 4K blu ray costs 2600. And lets not even talk about 4K player prices.
D. 4K movie rentals - even cheaper, costs around 150 bucks. This is the main reason I went for the box, though I have a Fire stick, PS4 and a OLED inbuilt apps already.
E. ability to watch my iphone 4k videos/photos directly on TV
Issues:
A. Price (also given its Apple)
B. No Kodi
C. No USB as mentioned above
D. Remote takes little getting used to (for non apple TV users)
E. Only one HDMI out and no Optical out, so people with slightly old surround sound AVR system cannot pass through 4K video through AVRs. This was my issue as well, but found a workaround with a direct connection between Apple TV>OLED and then used TV ARC to feed audio back to my AVR.
Hope this helps.