Interspiro Weight Kit
They are simple to install. Simply slide them into the preexisting slots located on the visor and snug up the set screws.
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.