COPIS vs APECS

fin

Suppose you dive with a helmet, an HP air source and a valve to add air. You have a completely DIR diving system as the only thing that is moving is tanks valve and you have full control on your air supply.
When you decide to use an on demand regulator (however simple) for breathing you compromise with the idea that it may somehow fail. I bet commercial divers of the past were also skeptical about OC safety. You just get even by adding redundancy to the system. Come to think of it, eccr vs mccr case is different only at the complexity as well as reliability of technology used.