Vasari grays are an amazing shortcut to values. Each of the grays we used were infused with a color form the limited palette to get the grayed off look you actually see when you are out in nature. You may not realize it, but when you really look they are there!
I am somewhat accustomed with the use of gray, I have alwasy tubed by remnants from my palette at the end of each day and then used that to mix with each color on my palette to neutralize the tube colors. Vasari paints are hand mixed and hand tubed, using no chalks or fillers. They may soon become my paint of choice. They do exactly what you think they will do when you use them.