Rapid shutdown is a safety function
Rapid-shutdown requirements are intended to reduce hazardous conductor voltage in defined parts of a photovoltaic system during an emergency or service condition. The exact requirement depends on the applicable electrical code and system design. A listed rapid-shutdown device may perform that safety function without optimizing maximum power point at each module.
Optimization is an energy-management function
A DC optimizer typically performs module-level power conversion or tracking so the array can better manage mismatch, shading or system architecture. Some optimizer platforms also provide rapid-shutdown capability as part of a listed system, but that does not make every optimizer interchangeable with every shutdown device. Compatibility with the inverter and system listing is critical.
Do not mix components by connector shape alone
Products that appear electrically similar can use different communications, shutdown logic, voltage windows and approved module ranges. Replacing a device with another brand because the connectors fit can create a noncompliant or nonfunctional system. Use manufacturer compatibility tables and the applicable code documentation for the exact inverter platform.
Compare the complete system objective
If a project needs rapid shutdown, choose a compliant system first. If it also needs module-level optimization or monitoring, compare the additional value and complexity of those features. The best design may use an optimizer that provides both functions, a dedicated rapid-shutdown device, or an architecture with other listed means of compliance.
Monitoring is another separate feature
Some module-level devices provide per-module telemetry while others do not. Monitoring can help identify mismatch or faults, but it should not be confused with the safety function of rapid shutdown or the energy function of optimization. Compare each capability separately in the product documentation.