I don't see any advantage over plain "-o 'ProxyJump box.in.the.middle'"? I guess this is supposed to buffer things? But then again, that's what "tail -f" is for…
Given a local machine and two remote machines: ssh remote2 -J remote1. This will connect to remote1 as a normal SSH connection, but then port forward a new connection to remote2 via that connection. Traffic leaving localhost is double-encrypted, and remote1 cannot see the data.
Disadvantage: remote1 must be able to connect to remote2. In this (ssh.beam.camp) software, remote2 can be in a place where accepting incoming connections is not possible.