King Kutter II (The yellow ones) are gear driven. No clue about the orange "compact" models.
A King Kutter tiller will work about as well as any brand in rocky soil. That is, NONE of them will take the abuse on a sustained basis. Have a few extra tines on hand, get used to horrific sounds of rocks bashing into the underside of the tiller, and be prepared for the possibility of broken u-joints, possibly damage to the pto drive train of the tractor, or worse. They will shake the living daylights out of tractor and operator when you hit a good sized rock.
Tillers CAN work in rocks. They don't LIKE to work in rocks.