I haven't posted much lately because of a family medical emergency, but I did find the time to investigate what it takes to load a book onto the Google Books/Google Play platform. Their interface is not nearly as easy to use as KDP, Nook Press, or Smashwords, but I managed to get Tribes loaded into their system.
Some early observations on the author interface are that it could really use some work. It requires an ISBN to even start the process, for one thing, as it uses that as an identifier for the book. Also, there are fields that need to be filled in that seem to rely on controlled lists, but the lists are not on a pull down menu; you have to type them. For example, the Book Industry Study Group (BISAC) subject/genre field. I had to find the online list to know exactly what to type. Also, the upload process is odd. It says basically "upload content" and you then upload the epub or PDF file and an image file for the cover, but there's not a specific place to do each. The first time I loaded the epub and the cover together and it only kept the cover file. I had to upload the epub again.
Finally, once the book is there, you can't see an online list of sales; instead you have to download a CSV file. That seems incredibly clunky to me.
I picked Tribes for this trial because it's standalone book, but when I have time, I plan to go back and add some more books, possibly the two Haven books. I got the idea to try Google Books from another author's posting on Facebook, so I will be curious to see how well the book does.
Correction: Google Books doesn't require an ISBN, but it does use it as a file name identifier, so if you don't have one, it makes up its own identifier.