Are these smart circuit breakers UL listed and safe to install in a US panel?

It varies a lot. The Leviton LB120-ST is a genuine panel-installed smart breaker with a stated 10kA interrupt rating designed for compatible load centers. Most of the inexpensive DIN-rail 'smart breakers' (DIHOOL and similar WiFi units) are designed around 110V/220V global wiring and DIN-rail mounting rather than standard North American breaker panels, and listings do not clearly document UL certification. Always confirm certification and have a licensed electrician verify compatibility before installing anything in your service panel.