This is almost exactly how I was taught to see value in high school art classes, and honestly, this is the only other time I've heard it. I think it's an awesome way to teach and I know that I improved a lot when I started applying this.
My intro to art teacher made us do something like that x3 She gave us all little pieces of paper and told us to draw the corresponding square. The only problem; I figured out what we were drawing and my brain went "LAWL, NOPE" half-way through. But still, this does work of a lot of people I know. So silly that something so simple can be so helpful sometimes xD
I could never do this on a grid (I used to have coloring books that had these exercises) but if you just gave me a nice clean sheet of paper I could do it just fine. I'm no perfect replicator but the grid doesn't work for me with this.
That said I love the color part of the tutorial (I have nothing against the grid method). I've been wondering how to do a picture with just one color's shades to practice shading.
Overall the tutorial is clear and concise. It's detailed enough to be helpful but simple in a way that makes it clear Thanks for sharing it!