My parish has been doing this for as long as I can recall, the priest leads it. In a former life I used to travel frequently and I liked to attend mass when I could. There were only two places I attended mass that finished with the prayer to St. Michael.
The first was McDill AFB in Tampa, I went to mid day mass several times. They had a big statue of St Michael behind the alter, made my day. The second was at Ft Leavenworth in Kansas for a well attended Sunday mass.
Thank you for sharing that. We sure could use some help from St. Michael. It seems as if there are more evil spirits prowling about the world seeking the ruin of souls than ever before.