This is an example of a flat gutter screen, and why it's a bad attempt at solving clogged gutters because the top just plugs.
You can see the effect of a clogged cap here, the water and junk just flows over the edge when it rains.
As you can see, the gutter isn't plugged - the the leaffilter sure is. No water gets into this system - it just runs over the top.
Most of the gutter guard systems on the market today are a variation of a flat gutter guard. They are meant to "cap" the gutters and screen debris out. The main issue with these is that without the ability to shed debris, stuff just piles up. This means you need to get up there and clean them anywway or you're going to get water damage from waterfalls.