This uses Tor's hidden services. The project page says each client makes 3 "random hops" and meet in the middle to create a secure tunnel. The communications never leave the Tor network so, I could be wrong, but I don't think traffic analysis applies here.

Tor has random hops, but no cover traffic, so black-box traffic analysis is trivial if you cast a wide-enough net.

Tor has cover traffic.

If by "cover traffic" you mean there are other users on the system then you are correct. If by "cover traffic" you mean internally generated traffic that can be used to obscure traffic between any two links (e.g. keep a fixed size bandwidth pipe full even when not in use) then you are incorrect. The former is of little value in thwarting traffic analysis and the latter is costly in terms of already limited system performance and imposes costs on participants that few are willing to bear.

Yes, it uses hidden services; I won't know x23ff...sds is you. However, the most plausible link between me and evgen is HN, so x23ff...sds appears on both of our contact lists, it's likely to be a HN user. More widespread analysis of contact lists can probably tell us who you are. (So you know evgen and me, but not RickRoll? That gives me a good idea of who you are...)

This is one reason why it'd be good to use different IDs for chatting with different people. Unfortunately, Tor wasn't designed to work that way, so you may need to run multiple clients or something similarly annoying to get this to work.