I also have the 4/slider. Due to the style of my garage I was unable to have the one panel extended to the side. When mine is opened up the panels do not leave full access...only 3/4 due to the panels being on one side of the opening.
Ventilation is the whole idea. While the black screen gives better ventilation due to the larger sized mesh, people can see in to the garage.
The white mesh has a smaller mesh and because of the color is harder for people to view the inside of the garage.
I prefer the sliders since our cat box is in the garage and I do not have to open a slider very far to get in and out..................my wife would be ticked if a pussycat got out.
p.s. In the summer the garage temp is lowered a tremendous amount when I use the screens.