IME on a trike, you are more 'vehicular' in heavy traffic and can't 'thread' so well due to the track width and, it has to be said, the less good visibility (you can't look over cars like on a DF bike).
The main downsides I find with my ICE 'S', compared with my Grasshopper, is the lack of front suspension which makes the ride a bit more turbulent at speed - mind you, the guys at ICE are working on that one

- and the lower average speeds (~10%). However the stability benefits on cack / fronst covered country roads, and the ability to go up hills a zero mph without balancing are definite plus points
