Just so you know, A thermometer test was performed on another forum utilizing the self adhesive strip taped to the outside of a glass carboy, plus a digital sensing probe in a thermowell placed into the center of the carboy, and an additional sensing probe taped to the outside of the carboy and insulated from the surrounding ambient temp.
Would you mind posting a link to that thread?
For what it's worth, I've always found the strips to be pretty accurate.