We have 2 kittens 10 weeks and 8 months both from the same parents but different litters. We have gone through the usual stuff to introduce them slowly different rooms, food bowls, litter trays etc. We thought we would try this has the younger one was mewing quite a lot and they seemed a little stressed. It may just be coincidence but the younger one is definately happier and we have been able to leave them with the run of the house together. This is after 3 days. We bought 2 so we have one in the main living area and one upstairs on the landing both plugged in and on constantly. The only thing I would say is they do smell a bit strange not massively unpleasant and bearable if it makes the cats happier.