Yes, the System Sensor 2W-B is a significant upgrade over the older 521B model. Not only does it feature improved detection capabilities, but it also boasts enhanced reliability and ease of installation. The 2W-B offers advanced features such as built-in drift compensation and multiple sensitivity settings, ensuring more accurate and reliable fire detection. Additionally, its compatibility with modern fire alarm systems makes it an ideal choice for upgrading older setups. Overall, if you’re considering replacing your 521B, the System Sensor 2W-B is definitely worth considering for its improved performance and functionality.