Interesting about the lack of information from a DS for this unfortunate guy - I got a loaner with TACC recently (my car is a "sensorless" classic S) and was playing with it. I made a similar assumption to the OP that it would work reliably in stop and go traffic, but once it was slow to recognize traffic stopped and the collision avoidance system kicked in - fortunately I was able to stop, but I think it would be a good idea to educate new loaner drivers about this issue.