This makes no sense. Why would you want a filter half-way down the entire run? It makes more sense if it were a filter to have it at the top, where it catches whatever detritus before it gets into the system, like with screens and the like they really use.
Further, doesn’t it make more sense if it were to overflow to have it happen at the top where if it goes over it’s going over the gutter, the eave, etc? With the collector box acting that way you have the overflow going over up next to the sheeting/siding etc and right down to the foundation. That’s a worse result than having it over-top the gutter. rflow were to happen, to downspout happen at the top, where if it happens it just goes over the gutter, away on not down the side of the building itself.
In other words, what are you basing the idea on it functioning as a filter/spill over device?
Which the website I referred to (a crappily written one I admit, but one that offered a quick and concise explanation) said the same thing as well.