We’ve tried single side. We mounted the stoker’s timing ring outboard of her largest ring so as not lose the triple chainrings. Only some cranks have enough clearance under the arm to clear the timing ring and chain. The real downside is that if the rear chain overshifts off the large ring it instantly jams into the tensioned timing chain that is running necessarily close to the large ring. You don’t crash because the rear end still freewheels but you are immobilized until you slacken the eccentric and pry the jammed chain out of the timing chain with the large screwdriver which fortunately you remembered to bring with you on your road test. The “texture” of the two chains ensures that they will jam together tightly. Rear-admiral in charge of Her Majesty’s Royal Dockyard ordered immediate reversion to conventional cross-over drive. Her patience was tested by numerous mosquito bites sustained while both hands occupied helping captain clear jammed chain to restore motive power.