We used to have Economy 7 Electric heating in one of the houses we bought. As you say it was warm during the day but soon lost heat and was cold at nighttime when we needed it most. They are economical in one sense but if you don't control the heat during the day you are not going to get the benefit at night. I was fed up with it, when the weather turned warm we spent a day sweating. You don't have a lot of control of it. We just bought an electric fire for the lounge, and kept the output down during the day. We sold the house and moved after 3 years.