M gainer or whey protein?

You can use both. Both of these prodcts are going to work a little differently. The protein is strictly for the your muscles to recuperate after working out. Obviously you can take protein at different times throughout the day. The weight gainer will also have a certain amount of grams per serving. The weight gainer is not just a subsitute for protein. The weight gainer is to gain weight. The protein is to help rebuild muscle that gets broken down while working out.