I know we've been here before, Denny. I tried the probe in a thermowell one time, at your recommendation, and the result was big swings in the beer temperature, and either cooling or heating running almost nonstop. Because of the much greater thermal mass of the beer compared to the air, by the time the controller registers that set temperature has been achieved, ambient has gone far beyond it in whichever direction; then the beer coasts in that direction, and the over correction cycle starts in the other direction.... My experience aligns with the theory of the manufacturers, and the experience of many other brewers. There is clearly, however, a set of brewers who get good results from probing the beer instead of the air, like Denny. So whatever works for you. But if one method doesn't, try the other.