I don’t believe anyone said they were not repeaters, they just don’t repeat reliably for the Xiaomi devices. It’s not the Sylvania plug’s fault. In my testing, Iris plugs, Cree bulbs, Osram bulbs weren’t reliable repeaters for the Xiaomis either.
Regardless, this should get you started.
https://community.smartthings.com/t/sylvania-smart-plug-is-it-a-repeater/130149
Edit: Well, I feel foolish linking a thread that you already commented in. Sorry