They are using a proprietary messaging over zigbee, it will not work with SmartThings. You will need their hub. See the existing discussion thread (this is a clickable link)
. We do not plan to ever have an open API so you would not be able to connect to other systems but we are working towards being compatible with Apple HomeKit in the future.
As far as the issue with missing neutrals, most UK members are using one of the in wall zwave micros which does not require a neutral, such as some of the Fibaro models. Then you can select your own switch to go with it, so you can have exactly the same kind of switch as Den is offering. And you don’t have to worry about Wi-Fi interference, which is always an issue for fixed location zigbee devices like light switches. 