Bosco, I upgraded to the dual door, so I have the experience of using both designs. To be totally honest, the dual dial door was only a marginal improvement over the single dial door - IMHO, as I controlled temps just fine on the older design. As Dennis has preached to us many times, it's really the upper vent hat that controls the temps; you just have to provide enough air flow from the bottom so the fire doesn't go out. I do like the dual dial door over the single, as I can start out with the left dial wide open, along with the top hat wide open, to get the coals going good, then can close down on both top and bottom vents to get where I want for the final temps. I haven't done any very low cooks yet, where one might use the smallest couple of holes on the right dial, but I have used the largest 3 holes a lot for most of my under 450F cooks. For serious high temps (500F+), I've stopped pulling the lower vent door out and just opened the left and right dials all the way and pulled the guru port plug out. Gets the job done and I don't have to fret loosening the seal around the vent door frame over time from sliding the door in and out.
Hope this helps.