Just my 2-cents.
I'd rather have a turkey cooker burner for supplemental cooking. It'll take big frying pans, if needed to brown up a batch of onions in olive oil. It'll handle boiled shrimp, boiled potatoes, corn on the cob, just to mention a few items that may not fit on the grill along with the steaks.
A Coleman camp stove (propane or Coleman fuel) is another good alternative. Top it with a griddle for some meals. With TWO burners, you can have a pot of coffee on one and boil your mopping sauce on the other. Or, fry up some bacon while heating baked beans, for example. When the grill's full of chicken, multiple secondary burners can help the cook get everything ready at the same time.
Personally I'd rather have the unencumbered shelf space beside the grill. And, I can put those portable cookers where they best fit for any given situation. Makes it easier when helpers aren't elbowing for room in front of the grill to work.
You can't have too many stoves/cookers in the backyard!