I have both mi tvbox 3rd gen and nexus player , with the context of self support getting China app to stream. I would say mi box is more flexible.
Performance wise, no visible difference
Without rooting
Mibox + wireless mouse+ 3rd party launchrr, you can control TV built app and touch Base app easily.
With mouse, no button is mapping to menu key , there is slight inconvenience
Nexus player without rooting
Mouse left /right click function as select ,no mapping on menu ,back
Remote control: no menu key
To get everything to work, one need to use those mouse and keyboard combination.
Hope this helps those that deciding what to get.
Sent from Motorola NEXUS 6 using GAGT