It’s a great idea if it works for you. You must also have the physical space to store all the note cards, which these famous author’s have and many don’t. I think their idea of handling the notes regularly is the key. How often do you spend time working through your notes? I don’t I don’t spend enough time and the few times I’ve done coaching the people NEVER spend time going back through their notes. PKM/Zettelkasten isn’t magic, you still have to do the work of going back through your notes and understanding what’s there.