I usually do this with my smb+reel, especially if I know im going to use it. If i dont have pocket space and want to bring a back up mask, I'll do this on the opposite side. Its protected behind the bp and streamlined. No real entanglement hazard. You can do this via the bottom holes at the small of your back as well.
I believe I'm using 6mm bungie and it is pretty secure. The middle of most masks usually is mostly silicon and very little glass so it wedges on the mask pretty well. I have a cover to protect the mask from scratches. I also recommending clipping a double ender for extra security.
View attachment 659747
Thanks!
What is this? (The vertical black strap with D rings at the end)
Is it the mask strap or some other type of additional attachment to the mask strap?