The sliders set the relative importance or weights between these criteria in a way that anyone can visualize. Just drag them back and forth. Generally people will set them roughly (or perhaps use the pairwise option first) then press one of the sort buttons that instantly reorders the criteria. Now they can see whether they are in the right order of importance with the right profile, and adjust-sort-adjust-etc utill they are.
You can see how this meets the "7 item attention span" issue: you set the weights within each group of related criteria independently, so the participants need not keep the whole matrix in their heads at once.
This same screen is available to set subjective ratings across alternatives. Even though there may be many more than 7 alternatives, you can rate them for one criteria at a time and use the sort feature to work in subsets. Imagine ranking performance on a criterion like handling details or creativiy. You can arrange people who have similar abilities in a region and then move down the list to pick up a different span. Again the key is getting people's ability in the right order.