I have been using another product for years, but having adopted two more cats (bringing the total to 4) there was a lot of friction. So after reading reviews I thought I would try this. I bought 3 plugins for different areas. They only arrived last evening and I plugged them in in three different areas. After an hour the cat that is the most growly was playing with her tail.
This morning three cats are laying on the same bed (away from each other) but there has, so far, not been any hissing. This may seem small but compared to two mornings ago when there was hissing and growling when any cat passed one of the rooms, this morning only a very small token growl.
I recommend trying this product out.