When I had my shortarm on a SuperQuilter frame, I chose to attach the leaders (pillow ticking fabrics) by Velcro because I could make them any width I wanted...I used 36, 45, 64, 80 inches etc. The original leaders were to be made wiht casings so they could be slipped on and off. That was a pain since it involved taking the bars off the frame to slide the leaders on. Also, the leaders would not stay in place when it came time to roll them up. I didn't bother to use middle leaders. No matter how wide the leaders were, the short leader was 12 inches long while the long leader was 22 inches long. For example, if I was doing a baby quilt, I might use the 45 inch wide leaders and have another project, say, a large lap quilt, on a different sized set of leaders in case I wanted to switch them back and forth. It is far cheaper to make your own leaders than to buy premade leaders.
Now with my Bailey on Gracie Majestic frame, the leaders are a dream to put on the machine. Again, I have made different sized leaders.