To be honest I don't really care for the artwork. There are better anatomy books and you can just time yourself if you really want to do that. The only thing I like is how it tells you how close you were to the drawing. Which can be a good thing but also a bad thing. The person drawing should look at their finished drawing and be able to critique it themselves and say what can be improved. To always have a program do that for you might hinder that. As long as the person knows that they should analyze their drawings and such I guess it's fine.
My observational skills may be great but I said nothing about my drawing skills