I incorporate alot of the rotator cuff excercises Poliquin suggested back in his Muscle Media days (a long time ago, in a galaxy far - you get the picture).
Currently I am using the cable and performing side sweeps out - pulley is waist high, left hand starts on the right hip and sweeps out in 180 degrees of motion. The upper arm acts as the rotational axis. MUCH more fatiguing than the shoudler horn. Same set/rep/rest scheme.
Also - I am not fond of the reverse movement, sweeping inward. Seems to be too much pulling and my bicep gets more work than my rotator/shoulder.
im not sure about how it works a muscle but i have a very similar unit i got from a chiro years ago and whenver i have a sore muscle, tightness, inflammation etc i use the elctrical stim machine..let me tell you this thing friggin works..i really dont think you can gain any size from it lol but for recovery purposes its great!!