I like this a lot (was actually thinking of building something similar)! Some feedback I have:

- When I log in with my Google account, my name is shown as undefined ("Hi, undefined!").

- It would be nice to quickly select/unselect all of my calendars (I have a lot, but only one I really need to use).

- It would be cool to select a date range and then ask it to spit out all availabilities based on my calendar without needing to manually select available times. Although I like the current opt-in way too. Just a thought, maybe no change is needed here.