Have to say, this project is excellent. Having never used NodeRed, it was relatively trivial to setup on my Raspberry pi 3b+ SBC board (following the instructions) and get going. I then wired up a pushover node, and voila, I now have notifications on my phone.
Essentially, I wanted to recreate the pushover notifications that you get with octoprint, and this worked a treat. It's actually more powerful, as the DSF-Event nodes let you look for specific changes with the Duet object model.
I used the DSF-Intercept node (with custom g-code added in the slicer) to check for layer changes and report when the first layer was started and finished.