Normal people understand watts.
Because they know what an electric heater is.
And using 2x to 3x more electricity means more heat in their room.
Also many countries have smart electricity meters with in home units which tell them exactly how many watts are currently being consumed and how much that costs them.
I’m going to push back on this with a simple example. Go to your local hardware store and check out the electric space heater section. There will be a wide variety of units rated for small rooms, medium rooms, and large rooms, based on square footage. The heaters will have a variety of form factors and physical dimensions. Many of them will have mentions of “eco” and “efficiency”. Every single one of them, and I mean literally, will be a 1500W heater (or whatever your region’s equivalent maximum load per plug is which may vary in 240v countries). Exact same wattage, all 100% efficient because their only job is to produce heat, with wildly different dimensions and text on the box. Customers will swear up and down about the difference between these units.
I had to do this after my gas costs went well above my electric costs. Maybe you are in a country/area where your hardware store doesn’t supply a variety of heaters, but at my local store, no two models were the same wattage.
Do they? Even I have problem nowadays with this, because they write 60W but it's a LED and it acts like a 60W bulb but it's not 60W. 60W is more like branding.
And using 2x to 3x more electricity means more heat in their room.
Also many countries have smart electricity meters with in home units which tell them exactly how many watts are currently being consumed and how much that costs them.