Digital ones are more accurate with a probe attached to the dead centre of the back wall about 2" above the substrate. I use temp gun as a back up and check the thermometers readings. In some tanks i dont have termometers, so i just use temp gun. It is pretty accurate when you point from farther away to cover bigger area.

Ultimately nothing is 100% reliable, it is all various degrees of accuracy. I never rely on just one gadget per tank. In incubator i have2 different brands of thermometers + controller build in incubator itself and im using my themp gun once in a while.