Some of them help. The closer it is to the ground the more effective. Won't do anything on a truck for example. They also help push a bit more air through the grill. Lots of trade offs using one on the street but anything is better than nothing.
These cars are generally too high for a splitter to do very much. It's more for appearance.
The biggest benefit is actually the little vertical piece of the stock performance package chin spoiler where it meets the wheel opening. That little fence makes a very big aerodynamic difference.
Informative video. Never noticed the difference in splitters between the GT and EB. Thought they were the same but guess that shows how much I pay attention to the bottom of the cars, lol