Honestly, I love the ACC on my Expy. It might be my most favorite feature (tied with the air-conditioned front seats). It's not infallible (I found out is pretty hinky on 2-lane, curvy roads ...car in front of you gets out of sensor sight and the ACC accelerates ...in the entry of an apex). But for fairly straight-line 2-lane highway or 4-lane interstate driving, I'm loving never really having to step on the brakes and reactivate the CC. Not particularly concerned with gas mileage (and I did get 24.2 mpg from Flagstaff to Mesa, AZ ALL using the ACC).
The one thing I do notice is that I can leave the ACC primarily enabled, but I have the option of essentially defeating it with the "distance button." I have a button on my steering wheel with a tight arrow on the bottom side of the detent and a wide arrow on the top of the detent. It allows me to pick 3 different distances ...for the ACC to kick-in at. I have actually played with that and while I mostly prefer the widest spread, I have adjusted it on interstates that weren't as busy as others. Pretty sure I (accidentally) turned it down to "nothing" ...and the collision avoidance system helped me avoid disaster.
I say all this that has been a HUGE skeptic of these high-tech systems. I'm a bit of an "old curmudgeon" that probably isn't technically old enough to ascribe that self-titling. But alas, even after only 10 days and ~1400 miles, I'm sold on these features so much that I'm much more confident in the predictors' songs & dances about self-driving vehicles. These features have come a long way.
(Note: I should disclose that I'm a bit of a tech junkie and have worked in IT for nearly 31 years now.)