I have a fluval 2+ in my 20 gallon and that is completely silent and with a quite a high flow rate aswell. I'd recommend one.
True but that depends on what kind of fish your keeping. If the person is getting small fish like tetras or something about that size then it would be fine because even on my long 20g I over filter with it and it because the whisper power filter 40 is what I use and it filters 20-40 gallon tanks.Although from my expierence is its not as efficient as some of its louder competeters.