[0] https://nedbatchelder.com/text/bigo.html
[1] https://nedbatchelder.com/blog/201711/toxic_experts.html
I'll double down on my toxicity by saying I didn't like the page layout. As someone with ADHD (and a declining memory), I need to be led through formatting/sub-headings/bullets/colored sections/etc into each detail or it all blends together into a wall of text. The longer it takes to make a point (visually and conceptually), the more lost I am. I couldn't easily follow it. The Simple Wikipedia page was more straight to the point (https://simple.wikipedia.org/wiki/Big_O_notation), but reading the "full" Wikipedia page thrusts you headlong into a lot of math, which to me signifies that this shit is more complex than it seems and simplifying it is probably a bad idea.
My experience is the opposite. I hate the colorful books with many little boxes, pictures with captions in floaters, several different font sizes on the page, cute mascots etc, where even the order or reading is unclear.
Instead I found it much easier to learn from old books made before the 70s-80s, sometimes back into the 40s. It's single column, black on white, but the text is written by a real character and is far from dry. I had such a book on probability and it had a chapter on the philosophical interpretations of probability, which took the reader seriously, and not by heaping dry definitions but with an opinionated throughline through the history of it. I like that much better than the mealy mouthed, committee-written monstrosity that masks any passion for the subject. I'd rather take a half page definition or precise statement of a theorem where I have to check every word but I can then trust every word, over vague handwavy explanations. Often these modern books entirely withhold the formal definitions so you're left in a vague uneasy feeling where you kind of get it, have questions but can't find out "is it now this way, or that way, precisely?". And I'm not so sure that these irrelevant-cute-pics-everywhere books are really better for ADHD at the end of the day, as opposed to distraction free black on white paragraphs written by a single author with something to say.