Yes it makes a difference. The ring is slightly larger in diameter, and slightly taller in height. You can use more charcoal, burn longer, or hotter, depending on your needs. It is made of stainless, so no need to worry about it rusting out. A great addition if you are doing long, slow, cooks utilizing the "minion" method.
I use the BBQ Guru on my 22.5 inch WSM, so airflow is not really a problem. Trying to keep it cool is more of a problem than trying to keep the temps up is. Hope this helps you.