Honestly, use it to sort your temps out, but order the one from amazon and bring that one from home depot back. Save yourself some money.
Make sure you know the temps at the base under the substrate, but shooting glass with a IRI temp gun won't be accurate because you're not supposed to shoot reflective surfaces.
I'm fine with the temp gun I bought, but If I ever need another I will buy on Amazon. I changed my hot spot to paper towels, and then the cool side is with a thin layer of eco earth. I raised the thermostat and have the temp now at 85 and am checking it with the temp gun.