I agree that the adjustable charge bar is a terrific improvement for the Lee measures. I use one in each of the measures on my various Loadmaster toolheads. I was responding to the suggestion to use an adjustable bar as the top element in a double disk setup, which I think MIGHT cause a problem for the reason I mentioned.
In the case of using a single charge bar for loading rifle cartridge loads, though, I'm not sure it would have as much volume as a double disk setup using the larger disk openings. Admittedly the double disks can only produce stepped variations between loads, but the various combinations of disk openings really can produce fairly fine steps, and probably will allow larger volume charges to be dropped with the Auto-Disk measures than can be done with an adjustable charge bar.
Personally, I tried using the double disk setup for 223 but eventually gave up and went to a standalone Redding measure. I use 50-case loading blocks (usually 4 of 'em at a time) to do the powder charging, then run the charged cases through a Loadmaster's final 2 stages (bullet seater and factory crimp die).