DC danger points are the junctions, it's best to be very careful and if it's at all busy, treat them like crossing a road, because people zoom along and overtake someone in lane one then cut in with no indication e.t.c, and the person driving like a dick can't see you because the car in lane one will be hiding you from view until he / she cuts across. Similarly when people head onto the road and they are coming off of the slip road they are not looking for you, this is not as dangerous as the people coming off of the DC though.
Personally though I'd still rather ride on a good dual carriageway with 70 mph traffic than some of the narrow windy busy 50 mph A roads with lorries that take up the entire lane trying to pass or zooming round corners.
I'm amazed when I see fools riding on the local A331 race trackdual carriageway.
They must be barking as there are several quieter alternatives.
The thing is if you're not local you don't know all of these little nice routes and navigating them can be very time consuming and very difficult if you're riding 200 – 300 km +. I've ridden long (200km) rides where I have made up a very good quite routes on minor roads however, it's increased my ride time by 25%+ minimum dealing with all the number turns, looking out for road names and signs, looking at a map and working out if I've made a wrong turn.