hi. firebacks do throw more heat into the room as they heat up and act as a radiator for the fire. typically an open fire only has radiant heat. is really not efficient(15%).but looks great.
the fireback gives more radiance but more than that protects the structure.
to get it to work right though, ventilation is a key factor- the size of the opening in the fireplace and the size and height of the chimney.
good luck with your fire and it would always be a requirement to fit a carbon monoxide alarm.

I would recommend looking into a Rumford style of fireplace. They are specifically designed to maximize radiant heat output. Sometimes, its possible to "Rumfordize" and existing fireplace. I did this with mine by dry stacking bricks in the fireplace mainly to bring the back wall forward and to angle in the covings. Study up on Rumford fireplace design to see what I mean by that. By dry stacking the bricks in the existing fireplace without demolishing the original firebox, I can always easily return it to its original condition.