So here it is connected to the lighting of Awngate. Well you can't see the connection as that is at the back, but the dimmer control is hanging from a hook below the layout (left). This allows the level of the light (provided by two 30W tungsten strips) to be varied nicely. Now I could have made something similar using a dimmer switch and pattress box (and indeed I have on a previous layout) but that would probably have cost more (this was just £7) and not been so neat - plus this can be used on any layout.
Like all dimmer switches it only works with incandescent bulbs (i.e. not fluorescent/energy saving bulbs), and only up to 300W total so if you had a lot of lights you might need to run them in groups to separate dimmers. However for my needs it's perfect! Hmm, I wonder if it could be used with a soldereing iron for temperature control ...?