Hi jale - those spacers look exactly like the ones I got from Diverite Express (now Dive Gear Express) years ago. They are pretty good and I still use them a lot with independent doubles. It is a shame that these are no longer readily available. A friend I dive with is an engineer saw mine and made an improved version that was deeper and looks to be a bit more stable.
The soft bands make for easier and allow the use of cylinders with different diameters.
I think that independent doubles are great. Easier to transport and truly redundant, compared to manifold systems. If you dive them correctly (use around 30% in the first cylinder then swap and so on) then even if there is a failure and you can't reach the failing side then you should still have lots of gas left to ascend. I think manifolds give a false sense of security. If a low pressure hose goes and you are holding on to an anchor line in a current with one hand and a camera in the other then you may lose a lot of gas before you can turn off the isolator valve or the failing side and may lose too much gas to allow for a safe ascent. I often do long deco solo dives and this is a consideration if there is no buddy to provide gas.
If dived correctly, independent doubles would likely need at least two major failures (equipment or mental) before you are out of gas.
For serious deep dives I use a rebreather and mixed gas, but independent doubles and maybe some O2 or rich nitrox for deco are ideal for a lot of the diving I do.
