In reply to Jamie Bankhead:
> What exactly does this give you over a conventional retrievable abseil?
Never seen that before but could probably work it out. From what I can make out in the video, it is better than the conventional method for two reasons.
1. The knot seems to have a bit of spring in it which if you are abing on dodge tat will reduce the pressure from any bouncing on the rope.
2. When you pull the slip knot, the whole thing pings out of the loop in one go meaning that you have less chance of a knot / the end of the rope getting snagged.
Of course there is still the possibility that a rope falling in its entirety will also snag, or worse still, bring down a load of loose choss. Conventional retrieval gives you a bit more control in that department.