I think, if the Burley fits, it would be a great first bike. Sorry to the Kent owners, but I would feel a lot safer on this bike than the Kents. With 500 miles on it, why upgrade? The parts should be like new. Brifters and more speeds would be nice but ...

Ride it for awhile to see if you like tandeming. If you do, then sell it and buy a newer bike. However, make sure you replace the brake pads, tires and tubes if they are not new.