Single Cylinder regulator setup 

Another great video with solid logic 👏

This is basically a standard setup but you're breathing from your octo and keeping your primary on a necklace in case of an emergency. At 40 inches the longest hose is still short, so you're not putting distance between you and the panicked diver. The only advantages are that you know you're donating a working second stage, and the backup is always in the same place. I get that a 7 ft hose can be a lot to handle for a some people, but that's why there is the 5ft hose option. It's routed the same way, except it tucks under your armpit instead of under a hose retainer or canister on your waist strap, so it doesn't require hose management. It's as streamlined as the option shown here, but it gives you almost 2 feet extra distance when donating. This also means the OOG diver can comfortably swim next to you. This seems to me like a half measure when going to a full measure requires no additional effort and very little additional cost. A 5ft hose is only about $5 more expensive than a 40in hose and all it takes is running it across your chest and around the back of your neck. If you want to have your long hose primary in yellow, you can still do that with a 5ft hose. They're available in yellow as well.

Purposely running a “yellow” primary or just happened to be the color?

What’s the length of the primary hose?