The Velcro makes it easy to detach the leader so you can attach it to your backing using your sewing machine, or pinning while sitting at a table. My first frame had Velcro. I tried to use it a couple times, but didn't see the advantage. The other thing was the hook portion was applied to my rail, so it was always getting stray threads caught.
It's really a personal preference, as is your method of attaching extra fabric or a leader. As long as you use enough pins or staples (!!) to have the tension even along the entire length, it's as effective as basting. Whatever is quickest and easiest. Also consider the time to remove the leader with your chosen method.