GPT-5.6 Luna costs 28x less than GPT-6 Astra for code review ($0.0041 vs $0.113 per review) but finds fewer bugs: 69 verified bugs versus Astra's 92 across 50 pull requests, with a 24% false-positive rate compared to Astra's 4%. Luna is suitable for everyday correctness issues but unreliable for security-critical code like authentication and permissions.
A code analysis tool integrated with Greptile identifies bugs through mutation testing in a payment settlement module, demonstrating security-first practices where code executes only on GitHub Actions runners with read-only access and no repository modification capabilities.