The 200K is rather urban by Audax standards but no worse than most rides you would take to, say, get out of London. After Redbourn it is generally much more rural.
I did it a couple of years ago and then at least the first two controls - one in the Chilterns (I cannot remember exactly where now) and Redbourn were not commercial controls so I ran short of calories. The pub at Arlesey serves food fast.
Last year I did the 100k with my son, which overall is a nicer route and I am doing it again this year on the Tandem.