Great idea if you want to place the sonoff switch inside a rail electrical panel. The adapter has 4 holes and mounting screws, I only need two for the sonoff basic switch. Maybe other models have 4 holes. I bought another more advanced sonoff switch with power measuring stats capability (at least advertised as such) and plan on using it with this adapter right after the wires exit the fuse, to see how much power any of my electical circuits use in real life. My girl always bothers me about not turning off enough lights in the house and I plan on showing her the LED lights are almost nothing in terms of electricity cost.