It is just difficult to treat the superspinatus tendon, for instance, with the other arm. let alone the infaspinatus tendon. You would most like rly cause impingement and rotator cuff irrational on good shoulder by treating the bad.

What's a low setting to you? Each setting is defined by depth of tissue need to be treated, each tendon (4 in rotator cuff) lies in diffrent depths to the skin. So settings should be changed depending on tendon treated.

Also there is the anatomical locations of the most efficient areas to place ultrasound head to reduce bone heating and induce thermal effects to tendon.

Thirdly, 4 mins won't make any clinical change in tissues because the temp of tendon and surrounding wont reach desired 39-40 degrees.

I think this idea might be a false economy but if your going to do it best to go on course or pay the wife to go on it.