Double layer PCB for stable reliability - The expansion board uses a two-layer PCB with pins on both sides, improving circuit stability and reducing the risk of bad contacts or unstable signal transmission. GPIO duplication for flexible use - Extends one ESP32 GPIO pin to two outputs, making it easy to reuse pins in smart home projects and providing a compact alternative to a breadboard. COMPATIBILITY IMPORTANT - Only suitable for narrow version 38PIN ESP32 without mounting holes. Not suitable for other versions. Two wiring options - Two type connections: pin header and screw terminal. Choose the connection style that best fits your project goals. Use scenarios - Scenario 1: Duplicate a single ESP32 GPIO to drive two sensors or modules in a smart home device. - Scenario 2: Quick prototyping or testing when a full breadboard is not convenient. - Scenario 3: Space-constrained ESP32 projects that require a compact GPIO breakout with flexible wiring.