The Amazon listing seems to have a picture telling you to put them next to eachother and that there is an alarm that sounds if the temperature between the two differs 5*.
So I'd assume the intended purpose is redundancy on the probe. Not monitoring two spots.
I actually just had an issue with this. My secondary thermometer was showing the tank at 76*.
My inkbird thought it was at 96* so it wasn't turning the heater on.
My redundancy was around overheating the tank either through the heater failing on, or the controller failing on. Nothing to cover failing and off! Oops
