No, the pony is on and the regs are pressurized. The second stage is secured like you would a stage bottle. I picked up a inline shut off valve for the second stage and a OPV for the first stage. This is to prevent an unnoticed free flow from occurring, especially at the beginning of a dive when I'm splashing off the boat and a brief free flow is most likely. To deploy I just pull on the reg and the hose pulls free and slide the inline valve open. I can also remove the pony from the back mount if needed as the Highland pony mount uses a cam strap on the pony. I like this setup because it's basically like a tightly packaged stage/bail out bottle and barring a failure there's no chance of gas loss plus I don't have to open the tank valve behind me to get air.
The Highland mount is very nice too. The bottles do not bang on each other, the pony is very rigid. Also, it's very easy to swap tanks, which was important to me so I don't get in the habit of leaving it on the boat because it's a pain in the ass. Since the hose and reg is tightly secured like a stage tank all I have to do is hook it on to my primary tank cam band and it's installed. I like your DIY pony mount, but I don't believe it would work well with my double cam straps. If I'm not mistaken I think your BC only has one cam strap which allows you to slide the pony cam strap over the tank.
I came up with the mask tether primarily due to the many videos and stories I've read of angry fish knocking a mask off someone's head. Aside from losing the mask, I would also lose my GoPro if it came loose. So here's how it works. On the back of my neoprene mask strap I cut a small slit right at the hem. I installed a mountable zip tie, the kind that has a hole in it for screwing the zip tie down to a surface. Add a dab of neoprene glue to prevent tearing. I put another mountable zip tie on the back side of my octo necklace. I took approximately 6" of nylon line and tied a brass swivel snap to both ends. On one of the ends I removed the swivel. This makes it easy to add or remove. If my mask and GoPro were to get knocked off my head it should be sitting on my neck or shoulders. The entanglement risk is minimal because it hugs the back of my neck and even if it did become entangled I could easily cut the nylon line. Here's a picture for reference. I admit that I likely wouldn't use it on shallow dives with good viz. But if the plan was to hunt AJ or Cobia I most likely will, just because of the nature of those powerful fish.
As far as a buddy grabbing the octo, they're not going to get far with it because it's on a short hose over my shoulder. I also did not zip tie the necklace to the reg. It's tightly secured with shock cord, but not permanently attached to the reg. I did this purposefully so that in the unlikely event something did entangle the octo hose I could pull the reg free from the necklace to untangle it. I also did it so in the extremely unlikely event me and a buddy have to do a true air share due to my primary failing the reg can be removed from the necklace and we can do a very uncomfortable air share. The latter scenario is hardly worth bringing up with the pony in the equation.
I know some would argue against having 3 second stages, but in order to to eliminate one that would mean I need to either use an AIR2 or flat out ditch the octo on my primary. I don't like either of those options. In an air share situation I want to breath on an identical second stage as the one I was just using before donating. I want independence from my octo and inflator. As for the latter option of ditching the octo, I would be really pissed if I found myself in a situation where I needed air and there was a whole bunch of it on my back, but I couldn't access it because I didn't have a backup and my primary failed for whatever reason, like for example a cuda just sheared the hose. I could crimp the hose to stop the gas loss, but it would be hard to breath from it. Not to mention on shallow dives or if I develop a solid relationship with a good buddy I may not bring the pony and therefore could be going back and forth installing and uninstalling the hose and reg.
I have never tried to capture a bubble with my hand and eye socket. This is something I'm going to have to practice to see how realistic it would be for me as a solid solution. Saltwater stings and remember the viz over on our coast isn't as good as yours.
