What's the difference between this and Termius, especially for those who are just ssh'ing into their home machines?

Termius is SSH client. Termux is basically a terminal emulator + package manager. You can run Node, Rust, Claude Code locally on your phone.

As an example - I used it to do Rustlings every day I commute on a subway. NYC subways don't have mobile network coverage, so I can't just SSH there into a remote machine.