[Boulder]

I like the ATV 4K a lot, but it's missing audio passthrough which means that Dolby Atmos and DTS-X are also lost, at least for now. TvOS 12 supports Dolby Atmos but MrMC cannot utilize that at the moment. Also playback of pure 24 fps video doesn't work properly because the device outputs then at 23.976 fps.

[noggin]

Thanks guys.
The Apple TV is one of the only boxes I haven't got!
What's its achiles heal?

 No HD Audio bitstreaming (5.1/7.1 48kHz DTS HD MA/Dolby True HD/FLAC content will be decoded losslessly to PCM 5.1/7.1, but no metadata is passed through) However Blu-ray rips with Dolby True HD with Atmos or DTS:X are unsupported AIUI.  The recent Dolby Atmos update for ATV4K was for the lossy streaming version AIUI.

You can't run Kodi, easily, on the ATV4K, only MrMC which is a fork with modifications to make it Apple App Store friendly (removing Python-based add-on support was the main change ISTR), or Infuse player.  (You can side load Kodi - but it's a non-trivial process)

The upside - which is significant - is that it supports Netflix and Amazon Prime in UHD HDR with SDR/HDR switching and frame rate switching, and there are lots of well designed TV viewing apps (iPlayer, NRK, DR, SVT, C More, Viaplay in Europe to name a few)  The integrated voice search is pretty effective too.