the main thing to know about a IR thermometer is it will only measure the average of what is in its spot, so if your measuring a component make sure the spot is contained entirely on the surface you want to measure,
for power electronics, e.g. a TO-220 package, you want to make sure the spot is entirely on the black body not the reflective pad,
if you want one where you dont need to worry about effacacy that may be in your budget, chase up a dual wavelength one, and it will do the corrections internally, no matter the surface, so it will always be quite accurate, as a conventional one can give quite different readings between the shiny heatsink and the black plastic at the same temperature,