Some gutter guards fail in the springtime. They give you good protection during summer, autumn and winter but in spring, fine particles of pollen seeds and bark penetrate the mesh. Finer mesh designs may be better at protecting your gutter in spring.
The quality of the mesh you’re buying is important. The holes in a gutter guard mesh should be no more than about 6mm. If the holes in the mesh are too big then you won’t have adequate protection. Also be aware that the holes must be large enough for water to pass. If your home is surrounded by pine trees then you may need a very fine mesh to protect against pine needles.
I have seen meshes as fine as fly wire. Small particles of dust and pollen will penetrate even the finest mesh. If your guttering is flowing correctly most of this dust should flush down the pipes when it rains.