Plug in heaters

Hi, I have been looking at wall mounted plug in heaters to put into the back of my house (the bathroom and back hall get very cold compared to the rest of the house) obviously I know running another radiator out there would be the best option but it is not possible.


I have been looking up wall mounted electric heaters online and 3 types keep coming up but I am unsure what is the best heating/ efficient option.

There is the electric oil filled radiator/ towel rack usually ranging from 300-900 kwhs in output.

Panel Heaters (usually called eco) usually in the 500-1000 kwh range

Infrared heating panels.

While I know how the oil filled radiators work I am unsure how the other two work/ keep a room heated. I would be running the heater off a timer to boost the heat coming from a centeral heating radiator located in 1 of the 3 rooms (bathroom, hall, toilet) total area is prob less than 15 square meters. 
Thanks