Update: based on other comments, I WILL seriously look into replacing the use of checkout. It sounds like these newer features are probably stable enough for the simple things that are being done in the blog post, and that updating the post will more it a bit more useful as a starting point for learning git.
I'm thinking of posting the modern syntax as an alternative rather than a replacement to checkout, but I have yet to investigate how stable things are now... will do when I have time.
But meanwhile, the checkout method is fine, it works, and it's well-established for many years.