I am not "blaming the dead". I am stating the truth, if someone isn't paying attention to their monitor(s) it doesn't matter how many they have. People have had haptic units shaking and buzzing a storm and ignored, others have ignored visual ones like Nerd/HUD as they flash and try to get attention as well. Is the argument of having one that is more intrusive in demanding attention worth a discussion? Yes, IMHO. However, you didn't say a second more intrusive type, you seemed to be focusing on there being only one. I disagree that a single one is inherently more dangerous than say having two or even more. If that single one goes inop, then SCR is perfectly viable as is bail out. Some potential failure points that may cause a single one to go inop would also cause a second unit to as well (those are in fact most likely also to force a bail out and SCR not so much). I am amazed at how many instructors don't teach SCR on the SW, it taking away a tool that is very reliable. Plus, I would disagree with your assertion "That's where either unit or diver errors don't rapidly progress to life threatening" in the context of SW specifically. Leaving oxygen shut off is universal CCR, same no sorb . But the SW isn't a unit that "rapidly progress to life threatening" compared to other CCRs'.