It's great in normal traffic, but not so good in traffic that is speeding up and slowing down very quickly.
Humans can see the traffic and cars in front of the one car the system is tracking and react beforehand, lifting off before the directly in front car even has started to brake.
I was testing it out in traffic today that was going from stopped to maybe 30-40mph and then back to stopped, all quite quickly.
One time the system was so slow to react it triggered it's own accident mitigation system warning! Luckily I was covering the brake and watching what it was doing so could take over before it was really needed.