Whether it is successful or not depends on the cost to Shake Shack of each free shake. I have to think it is relatively small and that it is offset by the profit from food ordered with the shake. Of the MU fans in today--me plus at least 6 others--all ordered lunch so it may well be the shake cost is a small deduction from profit generated by the accompanying food. Since it appears to drive traffic, that food would not have been otherwise purchased. Greatly profitable? Of course not. But somewhat profitable and a good advertising vehicle? Likely.