The mist is for people who wish to have no thick smoke, just right. Some say that "B" for cheap stand, but I can not share this opinion. Who wants to have dense smoke, the need to buy another fluid to halt. But the tightness of smoke. Although you get a room not on "zero visibility" but at a party or something you do not need this also. For normal lighting effects and normal breathing the smoke is most suitable. Price / performance (ie promised service) is perfectly acceptable. But as I said, who wants to have thick smoke, then other classes are more fluid. Highly recommended is the "P".
I need the fog including for fire drills and therefore use Class "X" = zero visibility.