I stream on Amazon all the time. The interface is annoying, but Netflix made theirs annoying now too. The cool part with Amazon is that you can add Starz to it (or Showtime). So I've been on it watching Starz, but they also have some good original series stuff like The Man in the High Castle, and of course, The Grand Tour.
If I had to guess, the Grand Tour alone could drive subscriptions of the streaming service for people who don't want Prime. Think international. Folks who can't order from Amazon, but want the content. Top Gear was popular around the world.