Got some bad news. They aren't repeaters. @razorwing posted that here a while back, and I confirmed it with Sengled support.
Here are some links to relatively inexpensive plugs that work as zigbee routers/repeaters:
https://www.amazon.com/SONOFF-Zigbee-SmartThings-Amazon-Needed/dp/B08GKK89QQ/
https://www.amazon.com/Zigbee-Philips-SmartThings-Google-Required/dp/B07SQGG8Z7/
https://www.amazon.com/Centralite-Outlet-SmartThings-ZigBee-platforms/dp/B07DFPYV4K/
https://www.amazon.com/DOGAIN-SmartThings-Compatible-Assistant-Required/dp/B08G46WWBB/
