I watched Engineering Explained's video on stop start, and learned that all SS systems do save fuel on the urban cycle. Not much, but it does work. However, there is usually a separate battery to supply SS needs and a heavier duty starter for same.
Let's fast forward 5-7 years when the OEM warranty is gone and your SS car needs that specific battery replaced? does it retail at Walmart for $ 67.99 ? not a chance. Does the fuel savings over 7 years pay for the new 'specific category' battery? not a chance. Does the environmental benefit of not running the engine for all those stops offset the impact of making a replacement battery ? I have doubts.
And lastly, and more important to the owner, does the SS fail in a safe predictable manner with no adverse running characteristic that would impede safe operation from a stop? This is why I feel the risks and total costs exceed the justification for the OWNER, but the OEM gets to brag about the fuel savings. All unscientific, Canadian Gut Feelings.