This seems to have quite a different purpose from other high level audio/music programming languages, like TidalCycles and SuperCollider. Those are used in the “LiveCoding” scene — coding the music during a live performance — and are fundamentally concurrent, letting you create multiple sequences and loops that run on their own until stopped or modified. Handel, on the other hand, is linear. I guess it would be more useful for, as the title says, composing. It still seems a bit limited since it only supports one sequence of notes/chords, akin to using only one hand on a piano.
it appears to support multiple concurrent sequences. did you see the examples? https://github.com/ddj231/Handel/tree/master/Examples