One of the things you might consider is the fact that no the bents do not exercise the upper body very much. Personally I think this is a good thing. On a DF bike you have to tension the upper body and arms to hold yourself up. That means the energy that goes to doing this is available for the legs. That IMHO means a bent rider can ride faster and further. Additionally it means that the back and spine are not subject to stress or torque. This is why so many people that cant ride a DF bike anymore have switched to recumbents. All this goes for both bent bikes and trikes.