I have been using the iCloud Photo Library for quite a few months now.
In an earlier post, despite it’s obvious strengths, I listed some things that bugged me about the service. One of those things was the amount of space used by the Apple Photos app. Even with photo optimization switched on, the iCloud Photo Library was consuming over 4GB of my 16GB iPhone.
After reading up on Google’s Photo app for a while, I much prefer Google’s approach to the client iOS app.