Here is what the FLIR ONE looks like, nestled next to my lab standard for temperature measurement (accuracy ~0.2C), a thermocouple meter from Sable Systems International :
Here is our constant temperature source, a circulating water bath with precision temperature control:
Which is easy to confirm temperature with the thermocouple meter:
Since distilled water has a high and known emissivity, it makes it an easy target to produce thermal images from that will be consistent over time (plus/minus error and resolution of the controller).
Here is a sample image taken with the FLIR SC 660:
Here is a sample image taken with the consumer product, FLIR ONE:
As I describe elsewhere (I will post a link to a review paper that will be in press in a month or so), the FLIR ONE product saves its default image as a composite of a thermal image with a haloed/outline image in the usual FLIR JPG format. So, if you have other FLIR software, you can extract the actual thermal image and do proper thermography on the image. If you don't have their software, then you are basically stuck with whatever the spot sensor tells you what the temperature is. I would not trust the spot temperature measurements. The software does not allow you to set the emissivity precisely or numerically, and distance and other parameters are not available. Use the spot temperatures cautiously!
SD of the error for the FLIR SC 660: 0.0873°C