Teaching also involves stating an idea - which the author forgot to actually do. If it is your article that I am criticizing, I'm sorry for being crass, but make no mistake, the writing is half-assed. An article whose primary piece of advice is to "focus on the datatypes", shouldn't avoid the word "datatype" until the 2nd to last header.
Truthfully, the article would be better served by removing the first and 2nd to last section and instead be titled "Why I dislike working with monads in languages that support monads."
A mechanical metronome will help with a visual indicator, but this smells like a classic XY problem to me. Your issue isn't that you need a visually distinctive metronome, it's that you are rushing the beat and need to break that habit.
Sadly, a metronome can only get you halfway in that endeavor. The real fix will be to practice with other musicians who can call you out on it in real-time. It is embarrassing, it is time-consuming, and it isn't fun, but it WILL break you of the habit and force you to play better. And make sure they call you out on it immediately. As in you do not get to continue the song once it is noticed, and you must start over like dying in a video game.