The other option for multi-room sync is AirPlay, on any device where that is possible (including wiim), so it’s pretty easy to solve multi-room audio these days.
Chromecast Audio lost the ability to do multi-room sync in a patent dispute with sonos
i'm not sure what device you're looking at, but i've got a wiim pro plus and it definitely supports airplay - i was just using it yesterday.
It seems like the newest and most expensive devices (WiiM Amp Pro & WiiM Ultra) do not support Airplay.
i had been considering an ultra to replace my tv soundbar, but no airplay is probably a dealbreaker for me.