It seems that in the e-ship they capture the heat from the ordinary ship engines (which drive the propeller) and then use that heat to drive the magnus effect c

It seems that in the e-ship they capture the heat from the ordinary ship engines (which drive the propeller) and then use that heat to drive the magnus effect cylinders. So it seems they get the savings from capturing waste heat, mostly. But who knows if you would be able to get the same or more savings if you capture the heat and just use it to drive another propeller.