Our tandem does not have fancy suspension and drivetrain arrangement:
So far it's been popular with the neighbors, our longest ride on it was approx. 45 miles on mostly flat, paved railbed trail. Climbing steep hills can be interesting, the frame is not nearly as stiff as I like it to me, bottom bracket tend to sway side to side as I sit and grind up the hills.
We've gotten it up to approx. 45 mph when going down some nice long hills, the brakes worked well, but more braking power would be nice to keep things cool temperature wise.
It's a far cry from a high performance tandem, but nice enough to scoot around at decent speed and effciency.
I like the fact that I could switch riding position with stoker if need to and not have to turn my head around to communicate with stoker.