It's a cool demo. Though, to my ears it's still a bit far from my dream of having something cheap or free I can feed more niche books I like and use to create an audiobook version of them.
That's still my personal TTS dream as well. Google's Read Aloud voice blows everything else out of the water but I've found by experimentation that it will only read the first three and a half hours of web page text.
https://vocaroo.com/1oOjiLNCagur