The more these IoT devices can do the more important it is to separate them cleanly in their own VLAN or comparable measures and block all outside communication.
If the devices stop working without their command&control servers as curaga warns then they are not worth having in the first place and should be discarded or given away with a big fat warning.
Little side-story to show other practical unintended benefits:
Some years ago I bought an amazon firestick exclusively to use the XBMC fork Kodi, and I was wise enough to block all connections but to my NAS.
Friends did the same, but forgot my recommendation to block all possible, so their OS got upgraded and amazon removed functionality that was required to auto-start Kodi. Firmware downgrades are also not possible any more.
My device wasn't able to update, so I'm fine.
It's not just about China for me. I want to be in control.