UK Wall Switch

You might want to start with the lighting FAQ for the UK. You’ll see that the Aeon micro that you link to is the first option there, and is on the official “works with SmartThings” compatibility list for the UK.

When properly wired, turning the light on or off at the switch will not affect the in wall relay’s ability to hear the next networked “on” command. All the wall switch then actually does is send an instruction directly to the relay. It doesn’t completely cut the power to it.