The Plant Booster system is intended for outdoor use only because the barbed fittings are not considered appropriate for indoor use. The water is supposed to always be on to get the most benefit from the way the system works. If for whatever reason a plant is moved off its device, or a tube was to come off a fitting, for however long you are away water would continue to flow onto the floor of your house, which is probably not a great idea.
HOWEVER, there are ways to use the system indoors IF you use a gravity setup from a limited size reservoir like a vase. In this way only a limited amount of water can spill, thus removing the risk of water damage. The size of the reservoir will determine how long the water will last.