For filming they are great! They not only balance the full face mask but help keep out unwanted light from the sides. This is typically a problem when looking into a video camcorders view finder.

Does the ffm need to be balanced. This depends on the user. Most users are not in the water long enough to notice a difference. However, professional divers who spend hours underwater will notice a slight rise in the ffm. This after hours becomes uncomfortable. The weights solve the problem.