My favorite part about this is the built-in event tracking. You can easily see even detailed things like whether people failed the signup, maybe one degree of tracking beyond, say, Mixpanel. Hopefully, this can easily be integrated into larger systems like the same.

I love the built-in SSL. --My only real concern, and I'm sure reviewing the docs further will help me understand more, is how I mirror users on my app so that I don't have to query the REST API for user accounts.-- EDIT: Looks like it's automatic. Even cooler.