Viable? When anub is on farm, yes. If you have stacked aoe classes such as rogues and dk's and adds die really fast already, then it's viable because it will get you through and to P3 quicker. You shouldn't do anything but LB adds and dps anub when they are up.
Now, since you are asking this question I assume you don't have anub killed, and you should not be anything but FFB.