Yet they are still rolling out the old ones which don't work if you change supplier, even though they spend a load of time suggesting you change supplier. Most simple electrical items come with a power rating in watts so it's easy to work out the current being drawn. It's more complicated for goods which don't specify the percentage at lower settings: For example a 900W microwave might have 3 or 4 lower settings which don't have the power specified. A smart meter might help to calculate that current. Another possible use is working out which fuel is cheaper for a specific task: Bunging a ding meal in the Microwave for ten minutes from frozen or in the gas oven for half an hour. But overall I'd guess the benefits are dwarfed by the costs of installing them nationwide.