Using a wifi switch

I'm looking to use a sonoff wifi switch for some kitchen LED lighting so I can then use Alexa to turn on and off. 

Because there are 3 sets of lights they all plug into a 4 way extension lead so I'm only actually using one of the kitchen sockets. 

Can I cut the cable of the extension lead and fit the wifi switch? 

That way all the lights work using the same wifi switch. 

There is only a live and neutral needed for the wifi switch so could I just connect those and not touch the earth of the extension lead so the earth still goes from the plug to the socket end? Although inside I was going to put the wifi switch and loose earth in a waterproof box so hidden. 

Any help or suggestions please? 

Many thanks. 

Instead of messing around with the wiring of the extension lead like this, why not just use a WiFi smart plug/adaptor?

That's why you're the qualified expert lol! It was just because I had two already to was looking to use them but I guess it would be a lot easier and I could use the switches for outside. Thanks mate.