Can't beat a solid nutrition and hard workout plan. Mass Gainers in my opinion are worthless and not needed, they are only powdered Macro Nutrients with bit of extras that should never take the place of Whole Healthy Clean foods. Look into your nutrition and learn to adapt Macros to fit your goals, kick up a solid workout plan and then think about supplements.
Want a gainer shake? Its cheap , buy cheap whey isolate , add Natural Peanut Butter , Almond Butter , EVOO , oatmeal , and bananas, thats your gainer shake right there , Protein , fats , carbs and fruit (more carbs) and pound it along with HEALTHY WHOLE MEALS, I suggest you look into the Nutrition Forum for recipes and tips on dieting , start up by calculating your BMR and TDEE (Basal Metabolic Rate and Total Day Energy Expenditure) And work from there with a nice calorical surplus if you want to gain weight. Solid workout plans for beginners are 5X5, Meat and Potatoes and Starting Strength , look into them too. If you need any help, just ask , we are here for that! Good luck and welcome to AM!