HI,
I have ridden the Redmount for about 2 yrs I have NEVER had any car pass close enough to hit with my arm - they tend to treat you like a slow moving tractor and they really skirt round. I think probably the biggest problem I have is that I get to a high speed (37.5mph - is my fastest so far) and I really resent slowing down at roundabouts and junctions, whizzing between cars going round the roundabout is FAR more dangerous than being low down.
I also have a flourescent jacket over the back of the seat - this flaps a bit and draws attention.
It is strange but once you ride one on the road - you lose that sense of risk + on my trike I have two great mirrors and I can see cars coming behind much easier than a bike...
Hope this allays your concerns a little.
Jonoffun