The Digital 4k movie can be watched in up to 2160p (4k) resolution (depending on internet connection and/or device) and includes High Dynamic Range increased color depth on TVs and devices that support HDR10.
Even if you’re not an Apple user you might consider downloading iTunes. Remember, Apple digital purchases are linked with Movies Anywhere so most of the titles purchased will also be available on other platforms such as Amazon Video, FandangoNow, Google Play and Vudu.
It doesn’t mean the 4k version will be available everywhere though — that would depend on the service. For your reference, here’s a list of 4k/HDR titles available on Apple TV 4k.