Timgr, your explanation for a dual master is exactly how I THOUGHT they worked (you can lose line pressure in one circuit and the other will carry you) but twice in the last few years it has proven not to be the case in reality (for me). Both were OEM dual masters on a 97 Jeep and 2000 Ram. I can tell you, one lost REAR wheel cyl/line crippled ALL braking ability. It was not a 50% reduction (though losing a rear should net far less than 50% reduction I would think), it was 100% loss in braking ability. Dead petal all the way to the floor. After those encounters, my mindset has flipped on dual masters - as you might imagine. I no longer see the reason to remove the stock style equipment, specially after my own dual install didn't result in OEM quality fitment (very likely my own fault).