The low end ones are fine. They are the greatest thing since sliced bread. You can aim them at any point on the engine and find hot spots if they exist. One of these also confirmed that my sending unit was goofy. I got a new sending unit and my guage worked perfectly, confirmed, of course, by my nifty infrared thermometer.
btb, I am not convince that HF one is the one you want. You want one more like this:
