I grabbed the new 3-19 Condar probe thermometer off of eBay. It was a good deal and ours is now 5 years old. I wanted to be sure my reported flue temps are reasonably accurate and that our old thermometer was not falling out of calibration. Ideally I should have drilled a second hole to do a side by side analysis, but instead I pulled one and inserted the other. The results are now in. They agree with each other. I've only tested up to 800F but both thermometers are within one tick mark of each other in this semi-scientific test. These same conditions showed a 200°F+ difference with Pen's new model 3-29 thermometer.
https://www.hearth.com/econtent/index.php/forums/viewthread/70117/P44/
https://www.hearth.com/econtent/index.php/forums/viewthread/70117/P44/