Product review (4 stars): Give it time to normalize
I should note that I'm not an HVAC technician, just a homeowner with an occasional lets-find-the-mildew-in-the-basement problem. But I was pleased to find this relatively easy to use device.

The min-max function and relatively fast response time make it easy to use this to zero in on leaks and damp areas.  Because you can see the values changing as you walk around with the probe, it's tempting to try the "getting warmer/getting cooler" game with your mold farm, but this won't work as well as a slower approach - the readings change as you watch, but the sensors still need time to normalize to a particular area (I stuck the meter in my fridge and it still read 64 degrees.  Well, I just needed to wait.).

The easiest way to tell if you're getting a real value is if both numbers are going up and down a little bit, but not making larger changes (in a draft-less space they might not change at all, but this is the real world).

I wish the meter had a beep that would sound when the readings were just oscillating within a small (or settable) range. It does beep to warn you when it's about to turn off, so I know it's beep-capable. It would also be cool if it did the wet bulb equivalence calculations for you, though I don't need that particular application.