If you're using the majority of Android streaming boxes, they're Android only. The Nvidia Shield is probably the Rolls Royce of Android TV streamers. It also has Chromecast support, so you can stream All4 that way instead.
The only advantage to Apple TV 4K, is that it offers 4K movies for the normal price. Does anyone know if this Nvida device does the same?
The nVidia device doesn't have an nVidia streaming service - so it would be using standard Android TV services like Google Play Movies, Amazon etc. to purchase movies, and their pricing structures will apply.
The Apple TV 4K has a few more advantages :
1. Dolby Vision as well as HDR10 support
2. Frame Rate switching based on content metadata frame rate with the forthcoming tvOS update, (Which will also include HDR/SDR switching too)
At the moment very few devices offer automatic refresh rate switching. Either they run at a fixed frame rate, or you have to manually switch in System Settings or by using external apps like TVHZ.
Netflix has 23.976, 25 and 29.97Hz content, iPlayer has 25 and 50Hz, the other UK catch up services are 25Hz, Amazon Prime is mainly 23.976Hz - so you want dynamic 23.976, 50 and 59.94Hz output switching.
AIUI the new FireTV 4K is supposed to do this too - but is not without issues.
The nVidia Shield apps don't use refresh rate switching (though SPMC and Kodi will if they are installed)
Once Amazon Prime is also on the Apple TV 4K - if it is HDR - then it will definitely be one of the best solutions out there in video quality and ease of use terms. The UIs on some of the TV apps are beautiful on the Apple TV too. The Danish DR TV app is gorgeous.
It should also run a fork of Kodi called MrMC from the iTunes Store. This doesn't allow Python-based add ons (that is in breach of the Apple iTunes store rules) but does include binary PVR add-ons. (You should also be able to side load a full Kodi if you are up to that level of hackery - though without the USB Type-C port you will have to use Xcode over WiFi to do so)