We recently were on a job where the homeowner had gutter guards installed. The guards deteriorated in the sun and very small bits of debris were allowed to fall through into the gutters over a period of several years. This debris accumulated and eventually seedlings were able to take hold. We are now in the process of removing these guards and cleaning the gutters.
For the price of gutter guards, most homeowners would be much better off just having our services performed annually or semi-annually. It will save you many hundreds or thousands of dollars up front, and being on a regular schedule can help prevent this sort of issue that requires a more in-depth and more costly initial cleaning.