With all the best will in the world, it can be really hard to get accessibility right. It's also hard to find the right answers. Sure there's the WCAG guidelines, but they're also quite difficult to understand.
With all that in mind, I'm always endlessly thankful for easy to read, useful guides like this one. I've been guilty of a couple of ARIA alert crimes in years gone by, but with a guide like this, I won't be committing those crimes again.
I'd love to see more content like this!