They are certified. In the sense that if the grid goes down it won't send electricity into it regardless of the settings you have. If you set it up to avoid feeding back energy it is completely transparent from an utility operator perspective. This is at least what the electrician that signed off my installation said and it works for the EU grid. Not sure about US or other parts of the world.

Remember: the best and easiest transfer switch is a physical interlock which costs $50 and doesn't wear out or fail, etc.:

https://www.geninterlock.com/product/generator-interlock-kit...

No certification required. Code compliant. Idiot-proof.