We revisit how product market competition affects real efficiency by incorporating informational feedback from financial markets. While intensified competition reduces product market concentration, it lowers the value of speculators' proprietary information, discouraging information production and price discovery, with non-monotonic welfare effects. Market feedback can reduce or even dominate the positive effects of competition on welfare and efficiency, especially under highly informative prices for production or heightened market uncertainty. These findings underscore the importance of considering product-financial market interactions in antitrust policy. Our results remain robust when we consider discount rates, investor welfare, and cross-asset learning.