This ain't rocket science..but seems to sound complicated when in fact is so simple.
The bungie necklace keeps your back up safe and sound. Keeps it out of the dirt, out of possible hang ups - out of harms way. You are always ready to take that octo in the event you need it.
Forget DIR, cave diving and such. It is the best system and the simplest system out there.
having seen MANY MANY octos dragged in the mud, sand and get hooked up on wrecks...... let alone crash into fragile coral. Use what ever floats your boat...but the best place for your back up is where you can reach it quick. Having it around your neck ensures it is clean and ready to use. As opposed to having it hanging and possibly have some crap in it cause you were negligent, may cause some undo stress in an already stressful situation.
I can bet that not many practice OOA drills with there buddy. Deployment drills, reg switching. If you do not you should. In a panic situation anything can happen, practiced you can control it that much better. regardless of bungied necklace octo or one that is stuffed in a pocket or hanging from a clip...
I would sugest to try the alternatives. See if it is what you prefer...
I speak from experience. I had my reg ripped out of my mouth, Did not see it coming. My instinct was to grab at my neck which took a second to deploy, one exhale breathe and I was breathing..I switched to a long hose after that day. For me, I feel that you are in more control having a longer hose and your alternate secured around you neck.
It also does not cost 10$. Go to your local out door sports store and get some 1/4 bungie, some tie wraps and you can make it for less than 1,50$ plus have more in case your friends want one made. Stuff costs about 50, 75 cents a foot....
safe dives