I liked the 10% @@@ example, demonstrated their point pretty well.

Also for anyone who speaks or is currently learning Chinese... I've been working on a multiplayer CJK word game that shares a similar efficient brute force style of learning to the author's approach (although presented via gameplay instead of tooling). Every turn you get a random character and must type in a word that contains the char in ANY position. If you like fast paced word games it might be up your alley: https://danobang.com/?game_lang=cmn