As all tanks here have two posts, I tendentially prefer to use two independent first stages, each with its own second stage.
One, primary, with normal-sized black hose, plus SPG and inflator hose, the other with just one long yellow hose (designed to be donated).
Both regs are identical (MK5+109 modified to BA). I have 4 complete sets, for me, my wife and our two sons.
Whenever, for any reason, a tank with two posts is not available, I always have tools with me, and I reconfigure the yellow-hose second as an octopus on the other "main" reg.
Till now, in my life, I had to do this reconfiguration just twice. One at Maldives, and another on the Great Barrier in Australia. And I did not feel fully comfortable relying on just one valve and one first stage, also considering that those tanks were too small for me: they were something as 10 or 11 liters at 200 bar, I usually choose a 15 liters at 232 bars.
So I carefully avoided to go into deco range which such a reduced setup. I think it can be acceptable just for very shallow dives, where in case of failure you simply resurface.