Nice slideshow. I remember some fun trips in a couple of those caves.
I'm not sure why the narrator thinks the frog is the "safest" vertical system. I wouldn't necessarily say it's the easiest to teach, either. It is one of the lighter, more compact systems, and is generally preferred for coping with on-rope maneuvers (rebelays, etc). It's also the most common vertical caving system (worldwide). But overall I'd say the Mitchell, Ropewalker and other standard systems are equally safe when properly used.