#1 not an issue in BM#1 if you screw it up and breathe a cylinder dry, you'll have another one
#2 if your 1st or 2nd stage fails, you can feather the valve - hence no less gas than in BM
#3 the valves are actually easy to reach
BM is geat in narrow spaces though, and SM in flat spaces.
#2 shut down post in BM, no need to occupy a hand or distract yourself with feathering, plus BM lets you carry more gas more easily period.
#3 I’ll give you that one but if you can’t reach your BM valves you shouldn’t dive BM
None of these make SM safer IMO.