My wife and I are both 72 years old with health issues. We have a da Vinci design In-2-ition road tandem which we love riding. I added a MAC 500 watt, high winding. ( extra torque) front hub motor and a 48 volt battery to our bike. It has three speed settings, cruise control and a throttle. The installation was very simple and easy. Our drive train is not altered in any way and it rides like a regular tandem. Most of the time we use the lowest power setting which can get us to 10-12 mph. We use the throttle, motor to even out or effort. Small hills and loop de loo's get a quick touch of the throttle and over the top we go. Steep hills get sustained throttle letting us go up some very steep hills as 7-8 mph. Some of our rides that we previously had difficulties with at the tail end of the ride, we now enjoy. I don't know what our range is since we've never used up more than 50 % of our battery capacity. Our longest ride has been around 30 miles. We never rely on the battery alone. On all our rides we peddle and shift as needed. The motor only comes into play when needed.
PS: With a hub motor it's much easier to get going from a stop or riding in stop a go traffic. Quick stab of the throttle and we're up and away! With power assist level three, we can cruise at 20 mph while peddling. Battery won't last long though at that level of assist.