Check the calibration on your thermometers.
Glass of Ice Water - Thermometers should read 32F (give or take a degree)
Boiling water - thermometer should read 212F (give or take a degree)
Whichever one is the closest to both of those points is the one that is most accurate. If they are all the same, then your grate temperature is the one you should be worrying about as that is the level that the meat is being cooked on.
As for the Maverick ET732. I have had mine for a year and it has worked flawlessly for me. My roommate ruined one of the probes by submerging it for an extended period of time underwater while doing dishes. I haven't babied my Maverick either and it still keeps going. I use it 2-3 times a week, and the transmitter usually sits on my deck bar (has a roof over it) for several days at a time through high humidity and still 0 problems with it.
*Weber Mini WSM* *Weber Touch and Go Performer X3* *Sublime Smoke UDS* *Maverick ET-732 * World's Fastest Blue Thermapen **Pitmaster IQ110*