You can see a few very common issues in this one video and it relates not just to this Leaffilter, but to all gutter guards that do not have enough slope to shed debris:
First, when debris piles up on top it can cause water to backflow into and under the roof. You can see evidence of this from the staining on the back of the fascia board the gutter is mounted to.
Second, It's completely gummed up with junk. No water goes through this product but "the gutter isn't clogged"
Third, in the valley you can see it's still dripping even though it isn't even raining. It's a big sloppy wet sponge that's still overflowing, indicating there's a pond underneath (that's really bad for the roof)
Fourth, looking at the face of the gutter you can see all the overflow marks. Looks terrrible, but it's not performing the way it was promised. This customer was so fed up she had us replace it. She's gutter problem free now!