It might be effective if you are often stationary for long periods. If you have lots of short stops then replacing the bigger battery could do more harm than any emissions. There’s usually a switch to disable it.

Rented a car recently where the engine shuts off when stopped at a traffic light, then starts back up when taking your foot off the brake. Did not like it.

Electric cars don't even need to be restarted. There is nothing you could start.

No, but I have noticed all the cars NOT restarting at intersections!

Honestly never noticed

Been like that for years where have you been?

Mine automatically does that , and as soon as I take my foot off the brake it starts up and takes off .