ptburnett68 welcome to SMF!
I have the older MES 40", replies above have noted that due to the inaccuracy of the Masterbuilt
, cabinet temp sensor, I use external temp probes to know exactly what what going on. This included an external probe for accurate meat temp and another for accurate inside cabinet temp.
Would I use external for a newer MES with meat sensing probe? YES at least for the first dozen or so smokes so that I know it is dead on. OR, I would place a electric hot plate with pot of boiling water inside the MES or at least close enough to test the MES meat probe at boiling temp, and make sure it is accurate. I would do the test every other smoke, or simply use another external probe thermometer. Obviously you can't test the MES cabinet sensor this way, so again I would be using an external probe as a backup temp monitor. Even with my old unit I use two probes or a probe and an analog oven dial to verify cooking temps. Knowing the cooking temp is very important, if your off 50 deg so instead of cooking at 225º your really cooking at 275º, can really play havoc with timing your smokes, and potentially result in meat either being not cooked or over cooked, etc. The first hour is important to me, so I record temps 3 times x 10 minutes and two times at 15 minutes, that is the first hour. 2nd hour I switch to every 30 minutes so that is two readings, and then I am at 1 hour readings from that point on, depending on what I'm smoking. If you take the time to log the first two hours, you will really have a good handle on exactly what your smoker is doing. You can also make notes on if you added wood, what the smoke is like, etc.
GL with your new MES
I also keep notes especially during the first two hours of the smoke to make sure everything is progressing like it should.
I note time, meat probe temp, outdoor ambient temp, external cab sensing temp, MES cab sensing temp, backup analog cab sensing temp (I have to open the hatch to read this, so I position it so only have to barely crack the door. Since opening the hatch is not good, I only take this reading once per hour).