Adjusting disk brakes is definitely harder than caliper brakes. The clearance between the disk and pads is just a couple millimeters, so you squint alot trying to adjust them. Mechanical disk brakes have one fixed and one movable pad, and getting the disk the correct distance from each pad can be tricky. If the disk gets warped, you either have to try and true it (often unsuccessfully) or live with a scraping brake. BTW, disk brakes on department store bikes are often complete junk and hardly stop the bike.