Google Assistant available for all, but HDR is exclusive to the Shield TV.
The NVIDIA Shield TV remains as the best way to experience Android TV and all of the 4K and HDR content it has to offer, and Vudu recently announced an update to its app that reinforces this point even more.
With the latest update to the Vudu app on Android TV, you can now stream HDR content to watch your movies and TV shows with brighter colors and higher contrast for an overall better picture. HDR content is currently limited to the Shield TV, and you'll need to ensure that you also have a television that supports HDR10.
No matter what streaming box or smart TV you have, Vudu has also added support for the Google Assistant. You'll be able to say "Play [movie/TV show title] on Vudu" from your home screen to start watching right away, and once you're in the app and streaming your favorite show, you can use your voice to pause/play what you're watching, rewind, skip to the next episode, etc.