That looks cool, I hadn't heard of Circles before. I want to check it out now. I'm curious if it somehow keeps your data private from the server owner. That feels like the missing feature in most federated, privacy-focused social networks.
Side note: looks like it's made by Futo; I hadn't realized they were working on something like that. I've been using another one of their apps, Grayjay for almost all of my mobile Youtube viewing lately. It works great.