Weight gainers work, but what they fail, purposely, to tell you is exactly what type of weight you'll be gaining. There may possibly be some brands/types that exist that are superior to others, as far as quality and ingredients, but most, if not all, are sugar/carb-based, and most times put more fat on you than anything else. Truly healthy and keep-able gains are slow to come man, no matter which path you take to obtain them. You might as well do it the correct way and gain them by increasing your intake, but keeping proteins higher than your carbs and fats. Many people may disagree and say 40/40/20 is always better for quick gains - but I like to keep it 60/30/10, or around there, and simply increase daily intake by a couple thousand calories or so. You could always add more carbs and fats if gains are not improving.