Not done that ride, but being a Fen rider all year round then I have some experience to share.
The route (which most of which I have ridden at some point) is all very open, the wind will play a big part in the day. All the roads are shall we say an "acceptable" condition, some better than others.
If you get with a nice group and take it turns to share the wind, then this will make the day a lot easier.
If you're into distance, which as you're contemplating the ride then you must be, then I would say it's a great one to tick off the list.
P.S we did the "Round Norfolk" last year which was 200 miles...bit different as it included the North Norfolk coast line, it's not happening this year but it's a great ride to do if they organise it again. Not the same company though.