just started my free trial--initially i find the UI inferior to and less intuitive than spotify but better than tidal. catalog seems deep, if not as extensive as spotify. ultra hd sounds great; hd sounds better than spotify, though it's not a night-and-day difference and there's less ultra hd content than expected. playlists are ok, though not as well-done as spotify--i expect they'll markedly up their game and add content as they gain traction, since amazon is very customer-focused and has long-term vision on their road to world domination.
Only if Amazon have off-line ultra HD. LTE is not reliable at some location and insider building. I would do hard wired streaming at home or off-line on the road. Doing away from MQA is good if Amazon can do 192/24 or at least 96/24. My Oppo HA-1 and 105D can't take MQA.
Logged into Amazon Music on Node2i,  HD option shows up as menu item. When you click on it it asks you to sign up
Aurender says they are in contact with Amazon and will update in the coming weeks.