I have been trying to understand some things about briar. Their threat model document states that an attacker on the same network can actually see the to/from m

I have been trying to understand some things about briar. Their threat model document states that an attacker on the same network can actually see the to/from metadata. How does this work in relationship to tor? I want to use it, but I haven't been able to get it to work reliably, so I haven't started trying to convert people.