So this morning my garage air temp thermometer was 79 degrees. Most of the stuff inside my garage measured between 77-79 degrees with the infrared thermometer as well. I turned the car on and let the seat run on cool for a minute. Where the best airflow was the seat bottom measured 68.2 degrees at the coolest point and varied to 70.2 at its coolest point in the seat back. The surrounding leather was 77 degrees. So while it definately cools, it's not going to keep an ice cream cake from melting.
When you jump into a car with the roof up, blacks seats and the sun beating down, i'm sure the interior temps will measure into the 120+ degree range. My leather portion of the seats can get over 100 degrees sitting in the sun with the top down! In those cases the seats may feel relatively cold when you turn the cooler on.
Of course this isn't a scientific study but it's all the energy i'm going to put into it for now.