I think the insulation keeps the heat toward the tank instead of below, and makes it more energy efficient. Just make sure to have raised footing on the tank to allow airflow or you could damage the tank and whatever surface you have it on.

I just have mine taped onto the underside of my exo-terra tank with the thermostat probe taped between the uth and glass. The thermostat is set to 99F and maintains around 93-96F on the bare glass and 88-90F on the substrate. Just remember different substrates retain heat differently. I use jungle earth which is really loose.