I have not tried Hammerspoon but I've skimmed through their docs, I'd say ultimately it boils down to: do you want to write JS or Lua? And do you need any of the Hammerspoon-specific features? I personally don't know any Lua and actually quite like writing JS, I don't think I need any of extra features HS provides, and with Phoenix you can still run a shell script and still achieve many things HS provides explicitly.
