#13 No conversation privacy in default scalable configuration. Anyone can see your to/from fields and bc #1 it's great metadata.
Need to verify how bad #13 is, I think you can mitigate but most people use a public channel. The header I think its technically encrypted BUT with a known public key so everyone can see whose talking to whom. I think you can get encrypted headers on the public channel but docs aren't clear and probably limits your hops.