If you just want one or two levels of payment for access to your site, this may not be what you're looking for.
If you have several different subscriptions, all with access to different parts of your site, this is the only component I have found with such a capability.
The only disadvantage of this is that if you want to have administrators manage the calendar they will need to do it from Google Calendars.
Its also worth noting that the addon Ninja Shadowbox was conflicting with this addon. I was unable to load the Overview module or NextEvent module while it was enabled. I had to disable them to activate the calendar, I have no idea how to fix this at this point.