I am looking for some recommendations on a high end 4k UHD media player, thinking of Dune, Zidoo or Zapitti. Any insight into these and why I should choose one over the other would be most appreciated.
There are various owner and discussion threads talking about the pros and cons of different devices.
In simple terms, if you want something purely for NAS / local storage playback the ones you have mentioned are all good, albeit with different niggles.
If you also want Netflix/Amazon/Plex/KODI etc you need to start looking at Shield TV / Apple TV, but in my view they are not as good for local file streaming (others may disagree).
Personally I have an ATV, Shield, ROKU and Amazon fire TV for app based streaming (I use the ATV in my dedicated movie room), and a Zidoo Z9 for media playback (having had a Himedia Q10 and Vero 4k previously).