I advise strictly against weight gainers, be it of ANY brand.
In order to gain muscle you need calories. 300 to 500 calories more calories than you can burn.
For an average skinny guy it is in the range of 1800 to 3000. Lets take an average of 2500.
In order to gain weight, lets say he needs to eat around 2800 calories and 50% should come from carbs. Thats 350gms of carbs everyday. This is on the high end. Most of you will need carbs in the range of 200 to 250gms.
You get calories from Macronutrients : Carbs, Proteins, Fats
Carbs are the cheapest.
Best sources of carbs are:
–Oats: You can get 66gms from 100gms cooked oats.
–Brown Rice: 50 gms from 200gms cooked rice
–Potatoes: 50 gms in 250gms cooked potatoes
–Cows Milk: 50gms from 1 litre milk
–Chappati: 60gms from 3 medium chapatis
–Dal: 50gms in 2 medium bowls
–Fruits: 50 gms 2 large fruits like banana or apple.
Grand total: 350gms.
All these carbs sources are complex in nature (expect fruits which are simple sugars-fructose) and highly nutritious.
For example dal, milk etc have high protein content as well!
You will find a healthy serving of fibre and micronutrients in them as well.
Most gainers are simply filled with dextrose/maltodextrin which are simple sugars and can be outsourced cheaply.
At the same time the quality of the protein is low. Recently there is lot of research that soy protein may not be good for you. You can check out thislink to know on how may not be a good choice for you.
Combine that with sucrose ( not good for your health ), and other artificial flavourings.
Now, there may be some good mass gainers in the market, using oats, or other better sources of carbs, high quality protein like whey and no artificial flavours, but do note these high quality gainers would be rather expensive, and you are better off getting your calories from food.