The major one that concerns me is who is behind them. Even if we trust that their encryption is not backdoored, there is a lot of information that can be gathered just from the frequency of messages and who they are between.
If it came out that a three letter agency was running one of these networks, it would not suprise me at all.
Yeah but you cant really obfuscate your message destination and timing without using onion routing, and really thats just making it more expensive to compromise and run. That said other things here do make it seem like a honeypot...
Its fully open source though, even the server. Might not be that hard to fork it and let people host their own servers.