The Mozzarella Sticks were previously tested earlier this year in select locations in New York, New Jersey, and Connecticut and come with marinara sauce for dipping. It now appears it will be offered at all New York Tri-State locations for the duration of the promotion.
The three for $1 pricing makes for a pretty good value given that competior Sonic only offers 2 mozzarella sticks for $1 during their happy hour.
If it does well, it's possible we'll see it nationally someday.