The Plant Booster system is intended for outdoor use only because the barbed fittings are not considered appropriate for indoor use. Also remember that 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 are prepared to make the necessary arrangements. You could, for example, set a system up in the bathroom, in the bath, or the shower cubicle for your prized indoor plants, so that they can be automatically watered while you are away on holiday. If there was to be an issue, water could drain away safely, provided you also ensure that the drain cannot be blocked by a leaf, for example.