It’s always recommendable to first do some research and ask around when not too knowledgable around zigbee. Sorry to say that, but individual expectation very often remain unfulfilled, especially when it comes to most Chinese vendors, as they do as often not comply with zigbee standards. Having the zigbee logo does not mean it is a certified device and even having a certification does also not necessarily mean compliance.
That having said, there’s high chances that whatever high speed mode they advertise is either nothing else than using certain zigbee features or a proprietary mechanism solely working with their gateway. Unless proven otherwise, I consider it as marketing hoax.
To really know what’s going on, it would require to sniff the zigbee traffic between the gateway and the device. This has already been done for other devices and it is know that there’s some messages exchanged which couldn’t be reverse engineered yet, as presumably some encryption or hashing is applied. A 10 minute sniff of communication with the original gateway would be very useful to get some deeper insights.
Other than that, there’s not much more we can do than poke around in the dark while any dev has the device in hands. I’m hoping to get one in the next days so hopefully, I might be able to tickle a bit more out of it.
Lastly worth to note, the device isn’t supported yet. As it is mains powered, some basic features are exposed and it is generally usable, but there’s chances that quite some features are missing.