I believe if you are willing to advocate for the purchase of certain apps you also must be critical when criticism is called for.
I am advocate of ebooks in education and we have an ebook (a textbook) in the Amazon store. We considered iBooks and Kindle books and submitted our book to Amazon because Kindle was cross platform.
I have read ebooks on many different devices and used the software supplied by several companies. My present frustration is directed at the Google Play Book reading experience. Ironically, I am using the Play Book app to read How Google Works. I purchased the book from the Play Store rather than from the other possible options because it was a little less expensive (if I remember correctly). The irony stems from reading a very positive analysis of Google success using a kludgy Google product.
When I read for “my work”, the annotation, highlighting, and any other processing capabilities provided by the reading environment are very important. It has been fashionable to all such activity “deep reading”. The Kindle experience is by far my favorite. The tools work effectively and the content generated while reading can be downloaded. I have found the Google Play experience (note I am using the app on my iPad) very frustrating. The tools seem unresponsive and the content cannot be exported. Given the options of working with different software, I would purchase the same content through another service.
Google should be good at this kind of thing, but the software has a ways to go before it serves the purpose of serious reading.