If you read that article, you'll see that a 2x dose 24 hours prior, with 1x dose the day of, and 1x dose every day until one say following, is sufficient to reach protective levels for anal sex. But for vaginal sex, that does require longer use as those tissues require more time to absorb the medicine.
In this case you're not taking it "intermittently," you're taking it in the immediate window surrounding exposure. If you're only having unprotected sex once a month or once every few months, then the 2-1-1 approach gives you effective coverage just during those windows. Studies going back as far as 2017 show it to be adequate.
If you're having sex on a regular basis, or don't think you'll have 24 hours notice of sexy time, then you need to be on a consistent regimen... and the research backs that up as well. But for infrequent, planned potential exposure, the 2-1-1 regimen is sufficient.