Aggregate data doesn’t mean no client side data. It’s possible they’re collecting aggregate level client data too. They could go further and collect data on individuals that is not identifiable or useful to law enforcement in any way. I can think of a few ways to get anonymous usage data that allows you to improve your service while protecting your users. I don’t know their scheme but they clearly don’t need overly invasive forms of analytics as they have a solid service.
Yes? I work in the identified healthcare data space, but work close to people in the unidentified space and even something as personal as health data can be obfuscated in such a way it’s impossible to trace back to an individual. Not to mention whatever they’re logging is surely many orders of magnitude less identifiable. They also have an entire page dedicated to answering these types of questions and concerns.