Related to Xiaomi, the company is also doing some sketchy things in the smart home space under their brand "Aqara". I use HomeKit in my apartment and opted for Aqara branded wireless buttons and temp/humidity sensors because of the attractive hardware and good reviews. The devices require a wi-fi connected hub, not too strange for things that use Zigbee, so I gave that a go.
Well, on cursory examination, the Aqara/Xiaomi hub was talking to a bunch of Chinese servers constantly. I didn't dive too deep into what all they were actually for. When I blocked the device from phoning home with my router, all the connected devices stopped working! None of the buttons or sensors would work, the RGB light on the hub couldn't even be changed. As soon as it lost the ability to ping its servers in China, the thing actually started strobe light flashing blue. Re-enable the outside network access on it, starts working again. This was totally antithetical to why I use HomeKit in the first place, so I removed the hub and paired all the Aqara accessories with a generic open source Zigbee hub (ConBee II) and added it to HomeKit with HomeBridge.
In the future I plan to give brands more scrutiny before investing time/money in them and granting them unfettered access to my LAN...