I like the extended rappel set-up in this video for its anchor clip part. You can clip in as you set-up, test your set-up, then un-clip from the anchor to go. It also is my favourite solution to the prusik back-up, keeps enough space between the back-up and the descender / belay device to avoid problems.

I’ve had some feedback about the setup in this clip from both places I’ve posted it: 

• A knot in an 8mm dyneema sling can weaken it by half its rated strength. This could be catastrophic if shock loaded in an anchor system, in this case falling while clipped to the anchor prior to rappelling. The 8mm is fine in this application with static (body weight) load of rappelling under normal conditions. A nylon sling would be a good alternative as would be a 10mm or wider sling in Dyneema.
• The failure mode of Dyneema has to do with knots and their internal friction heat as they take-up in a big dynamic event like a fall. In this case the knots are the girth hitch to the harness and the middle knot. There is also the potential for heat from the descender / carabiner in a long fast rappel.
• Keep the extension only long enough to give the space between the device and the prussic.
• Be aware of getting your hair caught in the device as it’s close to your head.

I’d posted this as I like the method but I use it with nylon slings. To me coming from 25mm tape slings anything smaller is great and so I don’t feel the need to go to the supper thin stuff. I’m certainly not climbing at a level where a few grams make a difference otherwise I’d refuse that second almond croissant at the pre-climb breakfasts!

It is important to know the effects of knots and various set-ups on the gear you use, how flexible it can be in application. I like the creativity of applying the gear at hand to solve problems but the more specialised / lightweight it is the more constraints there are in it’s application and durability. Learning this is part of gaining the knowledge that is climbing. Also the fun of deciding which gear to buy and carry.

Thin Dyneema slings have their place as a super light component of a dynamic system (with your dynamic rope). Perhaps where the misapplication comes is where they are used as a general purpose work-horse in many climbing applications like the slings of old.

It’s worth having a look at these clips from DMM on slings at anchors and how to break Dyneema slings for more detail.