If you don't mind reading some incredibly lowbrow stuff, check out the moral panic at http://www.sundaypost.com/news-views/uk/reckless-cyclists-snub-dedicated-cycle-routes-1.125884
I used to often ride the A90 instead of NCN1, as did many I knew riding the route at the time (particularly women, including SWMBO, who didn't want to risk the quiet and dark stretches of off-road path in winter for personal safety reasons).
I never had any issues with traffic on the A90 - it was always when I got into town (where the two lanes turned into one) that it fell apart.
Old, old video posted years ago as part of a forum argument about when & how often to look behind, but features the A90: