This topic has been on my mind lately because I'm looking for something easily mountable. I have three of the ones listed above. I tested all three last night and the two Accurites had similar numbers (2-3% humidity difference and 0-2 degree temp difference. Note: All three were placed on the cool side of the enclosure.
https://smile.amazon.com/AcuRite-The...er+thermometer
AND
https://www.amazon.com/gp/product/B01M252EWA
However the TH-100, had a 6-10% higher humidity difference and a 1-2 degree higher temp difference.