Zigbee is the same frequency worldwide, the only regional difference is the allowed transmission strength. The US allows for much stronger transmissions then the UK/EU do.
That said, the issue with zigbee is what profile is it using. I believe at least some of the Aqara model line were certified to the ZHA profile (the same one that smartthings uses), while the original were only intended to be used with their own hub and so are “manufacturer proprietary” and not guaranteed to work with any other hubs. Hence some of the quirkiness.
Voltage and wiring standards, of course, are a separate issue altogether for the mains powered devices.