I do 1 cup of this every morning.
No Cholesterol, fat, excess calories, salmonella...Extremely convenient, fast and effective. One cup has roughly 48g of pure protein. Chug it, wash it down with juice or water and be on your way.
As far as gaining weight, if you want to do it clean and healthy, meaning lean muscle mass, then this is a good supplement to a well rounded diet plan.
To 'gain weight' you need to have a caloric excess above maintenance. That is, if you consume roughly 2000 calories a day and have stayed the same weight, you will need more than that to gain. The excess calories should come from a combination of quality carbs, protein and fats. Combine this diet with a solid weightlifting program, you should gain solid, lean mass (weight).
Don't get discouraged when you don't gain as fast as you would like. Under best case scenarios and natural circumstances, a man can gain roughly 20lbs of solid, lean muscle mass per year.