A/C Center Vent Plug Set (LMC item) - anyone use this? Help or hurt flow?

[Katrina/10]

I saw that in the catalog, too. So I went to the hardware store and found some plastic caps, and covered the extra holes. I had always wondered why the factory had put two hoses on one vent, and when I turned on the blower, I found out why. By feeding the vent from only one side or the other, the air is forced into the cab at an angle. The air flow goes only to the driver or passenger, depending on which side you blocked. I would have gone back in and put two hoses on it if it wasn't so much trouble.