I have cycled along it Fenstanton to Cambridge, I found it a little scary and a thrill, those lorry's really can drag you along, my mph increased without doing anything!.(I'd say 'Suck you along', but I know someone will edit and quote that line.)
I didn't know it was a cycle route, is it? I'd seen the signs at the exits guiding you to exit and re-join rather than just carry straight on. I did it on a weekend and most Lorries were great at overtaking in the far, outside lane,even though we were in the 'hard shoulder'
I knew a keen cyclist who regularly used to commute Huntingdon to Bar Hill because it is so straight- (old Roman Road) and fast (he didn't die, he just moved away!) Anyway, once was enough for me, we took the longer country route part NCN51? back from Cambridge and thankfully the the guided bus route (Which they want to make the new NCN51) is there now to cycle on....until the buses get going or they sort out the slight flooding problem.
The country Village route as an alternative to the A14 is longer and less direct, country roads aren't always safer. The Cycle route along side the bus guided track could have been a nice fast route but its a loose graveltrack(due to cost) which does almost doubles the time over the 12 mile route, I found, than if you take the smooth concrete guided bus track! Plus it is quite open to the wind, but that is the Fens for you.
I recommend trying the concrete track before the buses get going! As long as you are ok with keeping to a narrow 60cm ish width.