Fish and/or shrimp can get into the overflow but not past the sponge filter or ground up by the pump. So, better then a Vuppa from what I've heard.
I have lost a fish when I forgot to open it when I drained water from the tank during a WC.
The sponge needs to be cleaned regularly but you might go longer then a week or two before cleaning is needed.
Fortunately, it is easy to open and remove the filter pad for cleaning.
That is about it. Quiet and fast acting. In the amount of time it takes to drink a beer your surface film will be gone.