Finally arrived from U.K.. Never use DPD. They will hand it off to Isis, I mean Aramex and you'll get it when the ayatollah thinks you should. No questions allowed.

This came with the Peak 9. When would I use it?

That's a safety leash. Inside the chicken loop there should be a little ring. That's the safety. One end to the harness, one end to the safety so the kite doesn't drift away should you hit the ejector button :D

Instead of my usual leash?

You can use whatever leash you want to use really. This kite just came with its own. Keep using the one you are used to, or switch leashes for this kite. It doesn't matter. I use my Flysurfer leash instead of my Peter Lynn leash for all my kites because I prefer the Flysurfer leash over others.

Thanks, I was a little confused about the chicken loop.
I use a PK leash. This flysurfer leash has a purpose specific to a style of flying I don't practice.
Again thanks.

The only real difference in leashes for depowers is the length of the leash and the connections on either end. They all do the same job of connecting to the safety line or the suicide loop on the chicken loop to your harness.