A direct-resistance heater uses around one unit of electricity to deliver one unit of heat. A heat pump can deliver several units of heat per unit of electricity, depending on conditions.
Worked example
For 1,000 kWh of useful heat at €0.21/kWh, direct electric heating would cost about €210 in energy. An effective heat-pump COP of 3.5 would require approximately 286 kWh of electricity, or €60. The theoretical energy difference would be about €150.
This is not a complete investment calculation: installation, maintenance, actual usage, equipment cost and suitability must be considered separately.