This. You don't need a PC at all, I don't have one, just a TV and a Shield, and GeForce Now works great for me. I just buy Steam games through their website and it works perfectly.
It does not look like I can use it from either my Chromebook or my TV (Roku or Chromecast), where as Stadia indicates that it will be playable on my Chromebook, Android phone, and Chromecast.