No, no, NO. BAD BAD BAD. I may seem like i am exagerating but IMHO, mortars are a very large waste of points. With the strenght of a bolter and worse ap, it has little chance of killing anything. That being said, most players, unless very lazy, will space their units out so mortars have no effect. I personally have had bad experiences with mortars. however if you play low LD armies alot (ork, tau) than mortars might be a useful asset.
Just my 2 cents.
Just my 2 cents.