Premiere Protein bars, premade shakes, and powders are surprisingly tasty(if a bit high in sugars), and provide more than enough energy, protein, fiber, carbs and calories for putting on weight. They are not a total meal replacement bar, however, as there are many necessary vitamins missing, but this is the reason for other supplements, right?
I personally stick with more natural foods(beans, rice, cheese) for my actual caloric needs, and take multivitamins for the stuff I don't get in an average day(careful with iron. It can be somewhat toxic over 125% dv.). Plus other 'normal' meals. Rice and beans supply amazing amounts of protein, etc., for a much smaller price tag, and without all the processing that goes into most bars, powders, etc. While still giving flexibility of adjusting any other parts of a diet.