This is a damper that helps keep the heat in the cooking chamber. This is a 2-piece slide which lets you evenly let the smoke/heat out or you can do cross ventilation (see video). This mod makes the grill much more efficient. It can add up to 4 hours of time to a full hopper of Kingsford...
Standard disclaimers apply: I get nothing from posting this. Just a satisfied customer.
What difference did it make to the amount of smoke flavor in the meat and/or the cook grate temp and/or cook times and/or charcoal consumption?
I may need to add one to mine as I have a fan mounted within a few inches of the exhaust port (to keep the smoke out of my screen porch) and I/m concerned I'm causing too much draw through it.
Now this is nothing more than conjecture on my part, but I THINK that being able to shut down the size of the vent on the back of the pit forces the smoke to spend more time in the pit and therefore more time in contact with the meat that's cooking in there, which SHOULD inpart more of a smokey flavor. I do know that it gives me a level of control that I didn't have without it. How much difference that actually makes is beyond my ability to determine, as I installed it shortly after getting my 1050. I think i installed it after the second or maybe third cook.
Sorry that I couldn't be more informative. I do know that I like the way it works, even if it just ends up giving me something else to monkey with while cooking. :D