As regards turning it on for a half hour, then off again for a half hour for 4 hours, why would you do that ? After the first half an hour, your room might be still cold, and you'd have to wait a half hour for it to come on again.
Best is to set the thermostat at the desired temperature, and let the system come on and off when it wants. If it reaches its desired temp after a half hour (or after 20 minutes, the system will turn itself off).
But in answer to your question, its cheaper to turn on-off-on-off for half hour periods than having it on continuously, but you might be cold.
You get what you pay for.