Sylvania Smart Plug— is it a repeater?

Yes.

There are two types of these plugs. They have the same model number but one of them ends with a -A. I can’t speak for the -A and some people have reported issues with it repeating the xiaomi devices but I have experience with the model that doesn’t have the -A and it repeats and works. I have also been able to map out my zigbee network with them and see devices routing through them.

Below is a link to a post where I referenced this.