A bit of duplication from the above posts but it is worth summarising the situation...
The big difference, as far as I can tell, it that Netstream 4C uses broadband internet for streaming Cable TV (which needs a subscription?) whereas EyeTV running on a Mac uses TV tuner - free-to-air and no need for internet.
We don't have a conventional TV in our house. I have been using a Mac with EyeTV for many years. I can play live TV and EyeTV recordings to my projector from the Mac but need to switch the projector input to play other media from the ATV4.
I have tried using airplay on an iPad running EyeTV for iOS to watch the show on the projector (via ATV4) but the quality is poor (it goes through 2 on-the-fly conversions and wifi streams). However, watching EyeTV live/recordings directly on the iPad works very well. That is all that I want from a TVOS app.