In my experience that section of the a439 is far more unpleasant than the alternative a46.
Neither is nice.
A 439 is downhill, you move at 25 mph, traffic moves at 40-50, relatively easy to pull out and turn right
A 46 is uphill, you move at 10-15 mph, traffic moves at 60-70, riskier to pull out and turn right
It could well be that I am used to the A 439 and no longer see it as a danger, whereas I have only used the A 46 once and felt a bit threatened by fast moving lorries