My 149 has a deck like that. (is that a 42"?)
It mows nice. It was missing this when i got it.
But since i have welders and ways to form the material i made my own.
Not bolted in like the factory, I welded them right to the deck.
But like the others have said, I didn't see much difference in the way it mowed.
I have heard some say those baffles help lift the grass to get a better cut.
Just make sure to level the deck like the manual says and it should cut fine.