I think the fire bricks help mellow out the temp swings on other cookers. I have had nothing but rock solid temps on my MAK. I don't know of the bricks would give much benefit.
Fire bricks are for cookers that cant get much heat and swing like tarzan. firebricks would concentrate heat where it whouldnt be and damage the =finish and it wouldnt be covered under warranty
I put a bunch in my MAK for a few overnight cooks last winter. Didn't make a bit of difference on the temperature variations or overall pellet usage. Just made it harder to vacuum out when I was done.
Now I just use them to weigh down the cover during storm season..