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Just looking between Chelmsford and Harwich as they're the bits I'm familiar with, it looks like a decent route.
Between Colchester and Wivenhoe it's routed you along the Wivenhoe Trail which is a compacted dirt track, doable on a road bike but not that comfortably. Just before the trail it takes you past the old heath rec a weird way along some footpath that I wouldn't choose. I personally just ride along the A134 a bit further north when I head that way.
Just before that on Berechurch road the route seems determined to keep you on the silly cycle path that keeps crossing the road. I always ride along the road itself, it's low-traffic and fine to ride and doesn't mess you about. e: streetview on this road is really out of date, it's been widened, resurfaced and all the foliage has been removed to get rid of blind corners since then.
Used http://cycle.travel/ to come up with this Harwich to London route
https://ridewithgps.com/routes/23522492
Any silly billy roads I'm going to go down?