The Analox O2 analyzer is the one I have seen the most of (by far) out in the field.
I got my own Analox after a trip to Hawaii where the shop I booked through met me at the dive boat with my tanks of Nitrox. The DM that brought the tanks did not have an analyzer with him. The boat did not have an analyzer. I had to choose between diving unanalyzed tanks that were allegedly Nitrox 32, or diving other tanks that were air. I used the tanks of air. And bought my own analyzer as soon as I got home.
Sometimes, dive charter logistics mean that you don't have any opportunity to analyze your tanks until you are on the boat and have already left the dock. Analyzing your tanks is too important (to me, anyway) to RELY on the boat having a working analyzer that is in good shape. That is why my Analox is in a small, waterproof Pelican case that I can have in my dive bag when I get on the boat. When I analyze, I will use my own. If I get questionable readings or mine is dead, then I will hope the boat has one and use that. If mine was dead and the boat didn't have one that worked, I honestly don't know what I would do (besides be royally pissed).
My Analox was a shop demo model and I don't know for how long. I keep it in a small Pelican box, and with the "sensor saver" cap in it. I periodically checked calibration against pure O2, to confirm the sensor was still good and it lasted me almost 4 years. And I have no idea how old it really was when I bought it. So, it analyzed tanks for me over probably 200 - 250 dives. The replacement was a bit over $100, if I recall correctly.
I have never tested for CO. I know I should. I just have not yet gotten off my wallet and bought an analyzer for that.
But, from what I have read, the amount of CO that will hurt you is somewhat dependent on the depth you dive to and, therefore, the actual amount of CO in your lungs. At 100' there will be twice as many CO molecules in your lungs as there were when you were at 33'. Hopefully, it's just 2 times zero.
My gut is that 3 ppm is fine for any kind of normal depth (even to 200'). Over 10 and I wouldn't dive it (which begs the question of why I have not bought an analyzer yet!). Over 5 and I would only be likely to use it if the dive were going to be pretty shallow.
One thing that I *think* about the Palm O2 analyzer is that it can only be calibrated to air. I could be wrong about that. If so, somebody please correct me.
If that IS correct then that means a couple of things:
The correct calibration for atmospheric air is frequently not 20.9. Depending on barometric pressure, ambient temperature, and ambient humidity, it can be as low as maybe 20.1 (I don't have my calibration chart in front of me). For me and where I live, it's often 20.5. So, the only way to really be sure of the Palm calibration is to calibrate it using a scuba tank that is KNOWN to be air. That will (should) be perfectly dry (i.e. no humidity) air and can be used to calibrate to 20.9.
In contrast, the Analox comes with a chart so you can see what the correct value is and then calibrate to that. And, if you are going to be analyzing tanks with high O2 content (above 50%), you can calibrate the Analox to 100% using a tank that is KNOWN to be pure O2. That will then give you a (likely) more accurate reading on this high O2 gases.
How much does all of that matter for normal recreational diving (i.e. Nitrox that is 40% O2 or less)? Probably not really a whole lot. The Palm calibration might be off by 1/2 a percent or so. Given how "rough" NDL calculations are anyway, having your computer set for a mix that is 1% off from the "correct" setting is not likely to kill anyone (unless they were going to die with a correct Nitrox setting anyway) or get anyone bent.
