The Mircom MIX-2251B indeed represents a significant upgrade over the MIX-1251B. While both are high-quality addressable smoke detectors, the MIX-2251B offers improved sensitivity and response time, ensuring quicker detection of smoke and potential fires. Additionally, it features enhanced communication capabilities, allowing for better integration into modern fire alarm systems. Overall, the MIX-2251B provides superior performance and reliability, making it an excellent choice for upgrading your fire detection system.