You can shift just fine while leaving ACC engaged.I have ACC with the manual transmission and it works quite well--it behaves very similar to the ACC I had in my manual transmission G37s. Automatically adjusting cruising speed based on traffic is great. Obviously the manual transmission needs to be shifted (thus disengaging cruise control & ACC) if the speed changes significantly, so it's likely more convenient on an automatic transmission...but I really like it. The blind spot monitoring is pretty great as well, for what that's worth. I didn't realize how much I'd appreciate the blind spot monitoring (it's my first vehicle with the feature).
I get there are mixed feelings about them, but I feel genuinely safer with both safety packages on the JL--very happy with my decision to add them.