Just want to add in some thoughts I had after reading this thread, there's plenty of great ideas here!
As far as how to "store" all this stuff underwater, I use double end clips for everything and clip it to my BC. Personally, I hate the lanyards, it just gets in the way. But people want lanyards, so that's why we include them. For the snoot the mounting loop is specifically made to be big enough for a double ender, and also the color filters have a notch made big enough for a double ender. For the aperture cards I use the biggest hole in the card and put that thorough the double ender. That's also why the IR filter has the large loop on it.
I also want to address where some people are using the snoot an saying that it's not bright enough, and others saying they don't have a problem with brightness even at high apertures. The snoot was designed for macro work at close distances. The further the snoot is away, the less light that reaches the subject because it was designed for optimal efficiency for close up use. This is a common issue for people coming form other snoots, as other snoots work at a much longer distances and when they use the Backscatter snoot, they aren't close enough. As a rule you should shoot wth the biggest aperture hole possible at a closer distance rather than a smaller hole at a greater distance. The optimal distance is when you move the snoot closer until you have a very sharp clear edge to the beam, this is the brightest transmission of light. If you want a softer edge, just pull the snoot back slightly. Keep in mid if you do this on land the distance is much closer than when you are in water due to the optics. On a recent trip to Little Cayman I snooted a pike blenny at ISO 40 f36 and wasn't even at full power.
Regarding the oval aperture cards vs. the circle aperture cards, I find myself using the oval cards the most. I usually have the snoot on an angle rather than being perpendicular to the bottom. This produces somewhat of an oval shape without a card or with the circle card because of the angle. If I use the oval card I can then rotate the snoot to either eliminate the oval and turn it back to a circle, or I can turn it 90 degrees the other way and exaggerate the oval shape more. This is great for things like nudis and gobies which tend to be longer than they are wider so I can get the light just on the subject and not the surrounding area by rotating the snoot with the oval card.
Great thread and I hope this can give some answers/insight!
Jim