For a new product to be profitable if it have greater marginal utility than existing substitute products.
Explanation:
The choice of the Consumer is guided by his preferences for specific products, the budget constraints, the price of the product , and the marginal utility of products.
A consumer always faces a budget constraint because the consumer only has that amount of money, that he can spend on things that he desires.
The consumer choice depends on the marginal utility of the product and its price. Because we know that as the marginal utility declines with quantity, the price of the product does not vary, a consumer will tend to buy as much product until the marginal utility of the product falls below the marginal utility of other substitute products that the consumer can buy. Thus the consumer will stop buying more of products when the marginal utility of an additional amount is less than the price of the product.
For a new product to be profitable if it have greater marginal utility than existing substitute products.