Since you are the one in charge of your mealworms' nutrition, you can make sure your mealworms are healthy and strong. However, with the ones bought in the store, you cannot be sure what kind of food were they fed and their quality can be compromised. The mealworms in the store can also vary in their age and you cannot be sure how old are they - with your own little farm you can make sure to harvest them when they are the most nutritious.