[Jeffers24]

It all depends how fussy you are about 1080p upscaled picture quality on a 4K TV with a 4K Android Screen resolution set on the Shield.

Android Kodi Krypton has no high quality Lancos3 optimised upscaling options.

Please read this thread about upscaling on the NVIDIA Shield.

Disable upscaling in Nvidia Shield? (4K/UHD)

If you mostly only watch 1080p content leave the Shield's Android Screen resolution setting at 1080p and manually switch it over to 4K when you want to do some 4K viewing.

The 4K Amazon FireTV does this:

Playing 4K Ultra HD Videos on Fire TV

I will be interested to see what hardware upscaled picture quality the new Apple TV 4K can output when it is permanently set to a 4K screen resolution.
Maybe they will have an option to Auto Resolution switch for optimal picture outputs. Who knows.

Thanks for clear answer