Are Matter or Zigbee CO detectors ready for prime time?

Barely. r/MatterProtocol and r/homeassistant threads on the Heiman Matter CO detector note that life-safety devices have been the slowest category to adopt new smart-home standards, and that local-control via Home Assistant or SmartThings still requires some tinkering. They're a strong fit for committed smart-home users, but mainstream shoppers will have an easier time with a Wi-Fi or Ring-connected Kidde.