PTT Balcony Stage Speaker System

It appears that most stores installed the GLI Sound System instead of standard sound system. Was this decision driven by performance effects or cost considerations? As far as I know, the GLI system was custom-built, and there are no comparable speakers available on the open market. Additionally, they reduced the dimensions of the Warblettes' and Bandboard's boxes, then added a notch along the top edge on both sides. What was the point of them doing that?‌