I was confirmed in the Anglican Church and later in the Catholic Church.
2 sort of similar Churches, but different on a number of levels. Anglicans don’t formally believe in transubstantiation, purgatory, prayer for the dead, the keys in Matt 16 being with the Roman Bishop and other differences as well.
Just as when we say “amen” before receiving the body of Christ, by going through Catholic confirmation, we are in a sense affirming our beliefs in all things Catholic.
This is not like hopping from one denomination to another. And each person should be convinced in his or her own heart that they are ready to accept all Church teachings to include her authority.