@tarponchik i keep bringing up the sensors used in rebreathers because they are literally identical to those used in analyzers. In fact, those that change their cells out early ~12 months, will usually rotate those old cells into analyzers. These cells have already experienced say 100-200 hours of use at a ppO2 of 1.2 ish, and then go into use as O2 analyzers.
Sensors die when they either become voltage limited, or behave in a non-linear fashion. You don't know that it is suffering from either of those conditions unless you test it both below, and above the circumstances of it's use. In this case, you test at 20%, and at 100% and use between 30-40%. You do'nt know by testing in air if the cell is limited because you have no way to validate the linearity of the cell.
Regarding O2. Allowing customers to calibrate the analyzer is frankly more dangerous than keeping an O2 tank for shop personnel to calibrate with since most people don't know how to properly calibrate, and if they aren't using a cal-gas for it, there is no guarantee that the sensor has been fully purged. O2 is a regular item in dive shops that are filling nitrox, so it's not like it's not already in the building
Let me add this. I use an el cheapo as long as you put the sensor in a zip bag when not in use they will last for years. my first went over 5 years. continous exposure to O2 burns then out.