Yup, right now we've only been able to build an integration with Google Calendar. Turns out building a near replica of Google Calendar isn't easy! Once we add more services, we'll open it more broadly and make the questionnaire less cumbersome.
As for the form, it almost felt like one of those RPGs, where you're basically forced to answer "yes I'll pay". I can only assume that this is done for basic research. What's good for you is that you actually capture the No->Yes flow, which means "No".
I used 2 accounts, as I don't like giving apps full permission to my calendar.
Good luck!