Just got back from a 30 dive trip in Cozumel, and I used the OxyCheq CO analyzer (~$400) on every tank. It was super easy to use and I'm really happy with the purchase.
The test procedure with the flow restrictor ($30 addon) is as simple as can be. The flow restrictor screws onto the sensor port on the analyzer, then you hook the other end up to your BCD inflator hose. Flip the power on and wait a couple seconds until the initial reading shows, then open the tank valve. Wait a few more seconds and watch the readout as the gas flows. Done. Close the valve, purge, disconnect. Takes less than a minute for the whole process.
My only minor complaint is that the included carrying case isn't deep enough to leave the flow restrictor attached to the analyzer. So screwing the restrictor on and off the analyzer for every test is an unnecessary time sink and exposes the sensor to potential splashing. A different case will solve that problem for my next trip.
I found most AL80 air tanks in Cozumel to be in the 3-5ppm range, which is the same as the ambient reading in my home. The highest I saw was a couple of tanks of nitrox that measured 7ppm.
A few other divers throughout the two week trip were very interested in what I was doing when I would bust out the analyzer. I hope I was able to educate a few on a subject they probably hadn't thought much about!
Having this device is great peace of mind, and in my opinion was an absolute must to purchase and get familiar with before my first liveaboard trip. I give it two thumbs up.