Also, I agree with you, Spencerian (or any other ornate script) is not the best for coding notes.
Of course, to each their own... (I love penmanship, and I'm fluent in several scripts, but I do my coding in Emacs, thank you very much!)
Gregg is very much a "visible" sound system from a time when people just needed to capture the conversations and later expand back into text with the aid of a secretary. That is, if you didn't mutate your shorthand for your own purposes.
That being said, Aaron Hsu's handwriting is beautiful, but not my cup of tea for thinking on paper--my initial reaction to his scanned pages was unpleasant because it wasn't what I was used to from my own hands.
And given how practiced his hand looks, I wouldn't be surprised if he was able to write this much quicker in cursive than I could write it in printed letters.