Yep got to agree that there is one major failiour point the neck o ring, but in all my time in diving have only ever seen a leak in one of these and that was straight after a service and was down to a faulty ring. I think the chances of the o ring failing are very slim.
Shutting down is tricky as a 15 Ltr on a STA keeps the valve out of reach. That is why the tank is set high on my back. I can shut down in seconds.
Another plus is if you need to donate air the 1st stages won't be over worked and less likley to go into freeflow.
The main reason I have this tank was for switching between my twins and single without having to strip my regs. So no extra cost for me
I also have a Beuchat Y Valve, another fantastic valve.
However if I was to dive solo or deep on one I would defo carry a side
Ali