Boy, this has wandered. My $0.02 for what it is worth.
I have had several Respironic machines fail before their time. Two of them quit developing adequate air volume at about two years of age. Had to argue with the supply company about it, as it seems the only thing their techs considered and measured was pressure. They look at you like a deer in the headlights when you ask about volume. If the machine can't deliver enough volume at the set pressure, guess what happens when you inhale..... New machine corrected my symptoms each time. Another Respironic machine developed a problem with the power inlet plug being very flaky.
I have not had these problems with ResMed machines which still tend to work fine after 5 years. Most insurance companies I have dealt with and heard about only want to replace the machines after 5 years of age, including Medicare.
For the quality difference, I will find a way to deal with the ResMed 24 volt operation. So far I have been using an inverter. But, I don't dry camp much. Considering efficiencies, I may look into a Dc - DC converter.
Unfortunately, since I am now living at 4500 feet, the doctors are saying I need O2 at night as well. This certainly complicates any chance I have of boon-docking without hook-ups or a genny all night. My current concentrator pulls 350 watts. There are portable machines that appear to use less, at a cost of course.