Good article. I'd say the broader points here are:

- the old adage "don't roll out your own cryptography" (even if you're one of the biggest conglomerate in one of the world's wealthiest country).

- not a single person I know use this secret chat feature - it's sadly still quite rare in Korea to meet a privacy minded person even (especially?) in tech-focused groups, people use Telegram (which might be worst)