don't know the exact make-up of the insulation, but the humidity in the smoker itself could leak into the insulation and thereby make it less than effective.
I've never like the "single" point probes like your talking about because they only show the temp at that spot in the smoker.
I like my polder(s) because I can move them to where I want, on whatever shelf I need.
Yes, they've fast reacting, but I periodically test my smoker "uncalibrated" know and it's +/- 5 degrees on average.
Hope that helps.
Smokin'