AppleScript: Cannot click Menulet (Menu Bar 2) for Third Party App
I encountered the same problem (the script infinitely spinning) in macOS Sierra. I spent some time using Automator and was able to solve it by modifying the script slightly:

ignoring application responses
  tell application "System Events"
    click menu bar item 1 of menu bar 1 of application process "Pomodoro One"
  end tell
end ignoring
do shell script "killall System\\ Events"
delay 0.1
tell application "System Events"
  click menu item "Start Pomodoro" of menu 1 of menu bar item 1 of menu bar 1 of application process "Pomodoro One"
end tell