Waste of money.
They are only as smart as the people that use them, that is if you check them constantly to track down wastage such as a light left on in the house.
The power companies tell you that they are free but they actually add £11/year to your electricity bill or £5.50 to combined usage bills to pay for them over the next ten years.
Bear in mind that they are not installed by qualified electricians, the installers have undergone a one week training course on how to install them.
Your household insurance states that if you have any electrical work done by an unqualified electrician then any fire or electrical failure is not covered by your policy.
That includes smart meter installations. There is a lady in the south of the UK who owns a burnt out shell of a home caused by a fire that started in the smart meter and neither her or the power company's insurance company will pay out to rebuild the property. This has been going on for over two years now.