The elaborate machinery of the Devon was intended to solve a number of the problems faced by riders of early Tricycles.
One problem was the tendency of machines with one driving wheel to turn in that direction as you pedalled, which made for erratic steering. To remedy this, the Devon had two chain drives to power both wheels.
A second problem was that the outside wheel had to travel further than the inside wheel as you turned, which meant that two wheels had to travel at two different speeds. If not, the inner wheel would jam and the Tricycle would turn over. To solve this problem, the Devon had a ratchet system that disengaged one wheel as you turned. This allowed the wheel to travel at the necessary speed when turning, but it also meant that you lost power on one side and had to be careful with your steering.
A third difficulty with Tricycles was that going up or down hills involved shifting your weight forwards or backwards, meaning that you were no longer in the most efficient posture for pedalling. The Devon was designed with an unusual pivoting swing frame intended to keep you in the perfect pedalling position.
Finally, despite the additional safety offered by a Tricycle, there was a constant danger of it falling over backwards. The two tails sticking out at the back of the Devon were intended to prevent this from happening.