It teaches great basics but it is a bit dated if you go farther. First, he assumes that the highlight will always happen on the plane directly facing the lightsource (on diffused reflection (matte) it does, but not the case on specular reflection (shiny objects)).
Secondly, because of the first point, he thinks that the terminator/core shadow has the most saturation of color in the form. This can happen on skin when you consider subsurface scattering, but on other else, it is false. You can still use it as a compositional trick though due to contrast of saturation.
Third, if you rely on Figure drawing for all its worth for your anatomy knowledge, you are screwed.
For what he provides, his books is still invaluable but you need other books to correct some of the thing he mentions.
