A regular thermometer is all you need to check effectiveness across the pad. Inlet minus outlet is what your're looking for. You can't accurately assess pad function by using a phone app, thermometer on the side of your house, or infrared thermometer. Humidity is simpler to measure than folks think. A good rule of thumb is that the dewpoint is generally constant for the day and equal to the overnight low, unless a precipitation event happens. Using that information and a psychrometric calculator, you can easily determine humidty metrics of all kinds.
The infrared thermometer is the most abused measurement tool on the planet. Very few people understand how to use it correctly. The picture above illustrates my point exactly. The measurement area is proportional to the square of distance (it's a cone, not a point) so the further away you are the bigger your error. Surfaces with lots of air movement are not measured accurately because convection changes the emissivity. Lastly, any surface with reflective material (like spinning fan blades, or water droplets, etc.) will also read incorrectly. Hardly anybody pays attention to that or knows how to adjust emissivity correctly. I always get a kick out of the Window World commercials where they show an infrared gun reading the temperature of the glass and the emissivity is set for a perfect black-body (0.95).
Somewhere I have a table of expected outlet temperatures for given temp/humidity combinations. I will see if I can find it and post it.