I have never seen this before, but one of the courses I have to develop curriculum for includes high school level trigonometry, and I am pretty fucking convinced that for learners (especially with LDs in math), the τ circle constant is conceptually easier to understand. The page is absolutely correct that showing a new learner the special angles with τ is a much simpler point of entry than the special angles relative to π (Figures 8 and 10).
Thanks for sharing!