You have an expansion tank built into the top of your radiator. I fail to see how adding a second expansion tank provides any benefit. It will let you fill the radiator to the top, add another quart to your cooling system, but when up to temp that extra coolant is just riding in the side tank, not any help to the cooling system.
It does permit a closed system, keeping air out of the coolant. But I’m not sure how much benefit that is. May help long-term corrosion control. Wont help the cooling system do it’s job to remove heat.