But Mike, that's you, you pride yourself on being a good emt and I have no cause to not believe you but we have tons of lazy providers who do not take pride in their care of the patient. To them it's you call we haul and I am sure you work with at least one of them.
The machines are designed at least to me, to be an adjunct to the patient care continuum and to help those lazy providers to do what they should be doing all along, which is look at the patient. If the machine shows a pulse ox of 72% then the provider is prompted to gasp, look at the patient and hopefully make a thorough assessment of the patient as to whether they are truly at 72% or if the machine is off.
Your experiences are anecdotal and valid in your situation, I'm not discounting that, but the manufacturers of these devices I am sure have put a lot more research and development cost and time into producing these machines than you or I have in hours on the street.