One of the key challenges with integrating with Office 365 is the incompleteness of the API. Features available in other calendar APIs - such as reminders - are nowhere to be seen, making it even more of a challenge to work with multiple calendar API providers. Furthermore, the Office 365 API, just like all the other major calendar APIs, also has significant shortcomings when it comes to protecting data as it works from an 'all or nothing' perspective.
Overcoming these challenges requires continual investment in time and resources, with plenty of development headaches along the way. That’s why we created Cronofy.