> I also added cool features like the ability to maintain a persistent ssh connection to the server for fast one-offs

rsync already supports this via OpenSSH's ControlMaster directive. Bonus, it speeds up every connection to that server rather then a single tool's.

> the ability to do direct remote-remote transfers without forwarding your ssh agent (by using restricted ssh keys on the receiver that will only execute a specific request signed with the key on your laptop).

You can control your agent forwarding in your local ssh client configuration. And with modern ProxyJump, you don't need to forward your agent at all regardless of how many bastion hops are between you and your final target.