I haven't used gainer regularly, never really needed to. I used the whey isolate powder to try and gain muscle without adding weight, and it worked really well for that purpose.
I will definitely work if you use it correctly. Shakes will not replace whole foods. Some people go from eating 3000 calories of whole food to 2500 whole foods and 500 calorie shake. You'll stay at the same weight if you do that. So, figure out how many calories eat in a normal day, then add 500. Stay at that level for a week or two and keep track of your weight. That is where you make changes and adjustments. 2 lbs. a week is the max you want to put on. 1 lb. is pretty good. Anything less than that you should up your food intake.
And yes whey can be a part of a healthy diet if you dont go overboard. Protein is the building block of muscle, so you want to fuel your body for performance. However, some people can go overboard with too much protein and start eating like a bodybuilder. Athletes need to have carbs for energy, and you also need to take in healthy fats. So, your daily food intake should be something like 50-60% carbs, 25% protein, 25%fat. Make sure you get your recommended amount of vitamins through whole foods - EAT YOUR FRUITS AND VEGGIES.
Some other tips to help you out... Get plenty of sleep each night. Don't run long distances (>1 mile), do sprint training instead. Focus on compound lifts in the weight room. Plyometric training once a week, speed training once a week, strength training at least 3 times a week.