I have been using Cozi calendar for a couple of years on a recommendation of a friend. I will probably continue to use it but more as a front end to Google calender and as.an app to create and manage lists. I began using the Google app as part of a general deission to get more out of my Google account, especially email. I have been generally please with Google Calendar, especially the flexibility it offers in setting up notifications and providing for additional inormation. The schedule display works really well only emphasizing dates that actually have an entry. It easily shifts to week and month displays, although the wider that time span the more difficult the display is on my android phone. Still it is pretty useful. So I set it up to publish iCal notices to Cozi an now I have the best of both worlds and other family members who prefer the Cozi interface and lists are happy. I am not overly fond of the Cozi lists since they don't work as flexibly as I would like. If you have not used Google Calendar in a while give it another try.
The comments above apply to this app running on my Android (Galaxy S5) phone. Impressed with its performance on my phone, I loaded it on my Fire HD. Entirely different experience. Most of the features I praised on my Android phone do not appear to be available on Fire HD. Here it appears as a very feature deficit primitive app. I am very disappointed. Clearly, this performance has more to do with Amazon's implementation of Android than any inherent problem with the app.