I think that’s nice from a devotional standpoint, since I like the idea of Marian devotions. I would presume they use some short consecration prayer. It’s the type of thing we occasionally see, with the priest usually “inviting” people to say such a prayer after Mass or during announcement time or homily time.
However, I doubt that the entire congregation is doing an individual 33-day or 9-day Marian consecration, which is a serious commitment and a giving of yourself to Mary. It’s the type of thing that might be done by a prayer group on a voluntary basis (for example, a Miraculous Medal Novena group or a Flame of Love cenacle or a rosary group or US Grace Force, etc.) but if you tried to get everybody in a congregation to do it, some would not want to because they aren’t comfortable with it, and others would find it too much of a commitment, and there would also be confusion about whether such consecration is required by the Church when it’s not. There’s also a school of thought that things like Marian consecrations, scapular enrollments, etc should not be done by general parish congregations or other large groups because many participants don’t really understand what they’re doing or why, and thus don’t practice the devotion properly.
