In reply to danp89zz:
As the video explains, as long as there is some dynamic rope in the system dyneema is OK.
It reminds you to not link yourself directly to a rigid anchor with dyneema, because if you do and then slip off the stance, even a short drop will put massive shock loading onto your body, and could break the sling.
Used as runners dyneema slings are fine because you have the dynamic lead rope to take the shock out of the fall.