Hmmm, I see. I have little interest in sm. But thanks, now I see what they are doing. From my kayaks I rig the wing, bp and tank fully and put it in the rear tank well and put a leash on it. Then I pull the kayak retention STRAP over it and buckle and cinch. My fins and mask etc are in the forward hatch or sometimes bungeed and stowed between my legs. I wear my wetsuit or whatever I am wearing. I flip around in a pirouette while still in my seat and unbuckle my rig and roll it into the water after partially inflating the wing. It is still on the tether line. I put my fins on and mask and roll into the water (if it is rough I may put my fins on before the pirouette and allow my legs to hang over for stability and balance), come up under my rig and essentially swim into it. Release the tank tether, grab the anchor/kayak leash line and away I go. Getting back in is just the opposite. Not hard at all. Everything is ALWAYS leashed until I put it on and BEFORE taking it off.
I used to and still do sometimes dive from my kayak with NO BC. This means, like in the sm video there is potential for loosing the tank and regulator. If the water is calm I will often just flip backwards in the kayak, my rig is prepositioned in the well, I do an overhead entry to the harness and then flip overboard. Getting back out, I remove the rig in the water, after clipping to the kayak tank tether, I get onboard and then flip the tank into the well and secure with the kayak tank strap. The rig is always tethered if it is not on me.
I do this because I had to, early on, do a couple of gear recoveries, fortunately it was shallow water. I learned to always tether everything if I want to keep it. I am not particularly impressed with that video clip with the sm system. Looks like a cf to me and high potential for losing a rig.
Like I said, I usually keep my mask and fins and other loose gear in the bow hatch, sometimes even another tank. But if it is going to be rough and I do not want to open the forward hatch then I use a short bungee tether riveted to my kayak that I pass through the fin straps and mask strap. In this case, while underway, the tethered mask and fins ride in-between my legs on that tether line. My paddle is also on a leash. Everything is always leashed/tethered.
I have learned to install flotation into my kayak. I was using noodles but those add weight so what I have done now is purchased two LARGE sausages. These are permanently slid inside the kayak and inflated. They kinda squished themselves into either side in the channel created between the seat well and kayak gunnels. They are sufficient to keep the kayak afloat even if it is flooded. I have practiced de-flooding in the pool, on the open ocean, dunno. I do have a small bailing pump.
The three kayaks I have used are:
1. OK Scupper Pro TW- big, fast, seaworthy, 16 feet long
2. OK Caper- smaller but similar to the Scupper, easier for me to handle and load, 11 feet long
3. OK Scrambler- the universal SCUBA yak, never bought one but have used them. Kinda fugly, ugly, slow but stable, 12ish feet long
N
If any of my dive buddies want to get one for themselves, I'll accompany them with one of my hardshell SOTs (if they will carry my tank). 
