Works great, my cats refused to drink out of anything but the fish tank and they started to use this as soon as they saw it. One cat likes the top of the waterfall, the other likes the pool at the bottom. It makes a "blurb" sound as air replaces the water in resivour and it made them jump the first time that happened. Other than that funny moment it is great. With two cats drinking it needs a top up about twice a week.
The pump is loud enough that if you have it in a quiet room with nothing else it will be noticeable. It is about as loud as a small aquarium air pump, not a big deal in house with kids, but some in a quiet apartment might not like the noise.