Thanks - that's awesome to hear! We're still early days and would love your feedback. Feel free to send me an email (james@oncircles.com).
It would have been a great idea to add a small price in the app store, as my core assumption was that people would not pay for a social networking app alone. Maybe I will change my assumption there. You don't need to answer this if uncomfortable doing so (or can send by email) but how much would you pay today to know the app is sustained ad-free?
Otherwise, we are fortunate to be funded by a single angel who gives us freedom to decide the path of the company. He invested with the recognition that the tides on privacy and social media are changing and that a more intimate, private social network would be a definite solution in the future (In his words, "the two most important parts of anyone's network are the closest circles and the fringes, so Circles focuses on the former").
Our next stop was to build a Circles designed interoperable chat that would allow you to send and receive messages to pretty much any major third party app. We would charge for this. However, right now we collect no individual data from our users and most user information is encrypted at rest, making it very hard for us to build any real ads mechanism.
In relation to group chats, there is a notable difference in how Circles are set up. In a group chat everything is shared to the group, and all the members are directly connected to each other because they are in that group. Circles in their current setup are closer to broadcast lists.