For pine needles you need a screen. But as coarse as it can be and not let through pine needles. The screen at an angle rather than flat (at an angle means sloped similar to slope of the roof, you do not want a flat shelf for stuff to collect on). Some screens develop mold under the screen and then they block the water.
Look through youtube and you will see and get some ideas. One video by a guy that owns a gutter company is shot initially with the guy going through a dumpster full of failed gutter guards. I would believe him.
I have them on the gutters in my DE home and one needs to blow the leaves off the gutter guards once a year but nowhere as bad as cleaning a gutter.
Inside corner likely to collect stuff.
Here is the one I was referring to and another one with a different point of view:https://www.youtube.com/watch?v=0SSjRTMiUVUhttps://www.youtube.com/watch?v=pQ42ppZxxYU