Glasscages.com - Overflows

Looking at the section of "freshwater" overflows... What are thoughts on the efficacy and usefulness of the horizontal overflows. They seem somewhat akin to the hang-on-back 3rd party overflows, such as those from CPR.

They seem attractive from the standpoint of them being much less obtrusive, but what would some caveats be, if any, to a built-in overflow like them?



-Jason