I'd want to warn you, a bit.
What I've learned from past experiences, and yet again. There is a pass on cost to other systems.
While trying to figure out how to resolve this issue, without me having to book in the car for the whole day and be without transport. I've learned...
1 - The battery in the car is not a normal car battery. It can cost three time the price of a car battery and only have about the same life expectancy.
2 - The starter is also a different starter and can cost double the price of a normal starter. But just as a normal starter can last the life of the car.
I don't know if there are other things also.
Basicly, You do save petrol (gas) by the car shutting down at stops. But are the cost of petrol that are saved more than the increase in cost when it comes to maintenance?
Something interesting and useful...
You can brake without enabling the i-stop. i-stop only engages when the brake is completely pressed in. Useful when you do a quick stop, like at a stop street.
Lifting your foot slightly would also cause it to start up again, while the brakes are still engaged. Useful when you want full power/high revs when you lift your foot from the brake.