According to my contact in the OBD Eleven team:

Very cool. I did not want to buy an android device solely for this purpose.

I think you should give it a chance. The clunky behavior is when you break too hard before you let it come to a stop. I've tried to get the hang of it and as long as you bring the car to a standstill by feathering the brake, it won't shut off. Then once it's fully stopped, you press the brake harder and the engine goes off. It's possible to stop it smoothly and control exactly when you want the engine to go off.

What you're describing is how start-stop should work. It doesn't work that way in the S5. It is impossible to drive smoothly in California traffic, and trying to treat the brake pedal like an eggshell only makes it more frustrating.

Try shutting off the auto start stop and see how smoothly you can brake. I tried a few times, its a bit better but stop not smooth due to the performance brake pads.

I did it again this morning, I was used to stopping smoothly in the A4 a certain way but the S5 simply requires less brake pressure to slow down the car without shutting off the auto start/stop. It really does work, in traffic. If you need to slam the brakes all the time and leave only a couple of feet in front of you at all times then yes, it might be a problem, but in regular driving I think it's fine.

I tried to make it work, but ASS makes the car awkward and unpleasant to drive in traffic. I gave up after the car would repeatedly stop and start while crawling along in stop and go traffic. My mileage is nearly as good as it was on my previous A4 without ASS, so I do not feel the need to compromise the car's driveability.

I just changed jobs and get I sit in a lot more traffic, so I’m using traffic assist ACC a lot more. If you have Prestige / ACC and it’s enabled, ASS doesn’t engage at lights or traffic. I figured this out yesterday sitting on NWHWY for a long time.

I don't like the way the car drives with Traffic Jam Assist or with ACC in traffic, so I reserve ACC for extended highway drives, not for normal commuting. ACC doesn't have enough awareness in traffic and does far too much unnecessary acceleration followed by rapid braking, whereas I coast and use far less aggressive throttle and braking inputs. I'm glad I received a pretty decent deal on a Prestige because I really have only derived value from the HUD, overhead camera, and adjust ambient lighting.

What driving mode are you usually in? There is a vast difference between Dynamic and Comfort. For me, Dynamic is way too aggressive and Comfort is way too relaxed. ACC in Auto mode works quite well for my daily, heavy traffic commutes.