This is a new product from MistKing which rather than spraying at specified times throughout the day, it will spray when the humidity drops below the set percentage; similarly to how a thermostat controls temperature.
Here's what the manufacturer says about their product:
New product that works with any existing MistKing system. This controller works by constantly monitoring humidity on the probe. Based on current reading and required humidity HT-24 will activate the misting system as needed. Excellent choice when desired humidity needs to be achieved. It plugs directly into the 24V misting system power and not into an electrical outlet. As with any humidity probe based controller ensure that you do not spray directly onto it as it will give you unreliable performance.
Main features of MistKing Hygrostat Controller HT-24