That little overflow box looks good, first because it would be easy for one of us to add one to an existing tank, and because it is so unobtrusive. It would also be very easy to keep the inside clean, compared to the full tank height ones. If there is a major disadvantage to it it would be the very small length of the overflow, compared to most of the others. I also liked the little corner one they show, in an acrylic tank, for its unobtrusiveness.