I have purchased these historically for the greenhouse on Mill Green allotment and for the Space Saver greenhouse in the back garden.
I have one placed at the apex of the greenhouse with the outside sensor hung on the fence beside the greenhouse as a direct indoor out door comparison.
Then I have cable tied one at the top and second tray levels in the middle and taken the external sensor to the side walls internally so I can see the temperature variation within the greenhouse, as the sun travels across the front and the greenhouse goes back into shade.
They also provide me with information about where the hot spots are and how the reflectors at the back of the greenhouse affect the temperature
Another six of these have been purchased today, two more for the Space Saver and three for the new greenhouse for Spencer Road Allotment and one for the grow station in the shed.