Seemingly everyone has an opinion when it comes to gutter guards. Home Depot, Costco, and numerous other retaliers have supplied the do it youselfer with a range of plastic, metal, and foam gutter protection, these products perform differently and vary greatly in design. Some work pretty well, others don't, and some can actually void warranties on your shingle roof.
Having cleaned thousands of gutters we have seen it all. For a long time we abstained from installing any sort of gutter protection because we simply weren't confident about long term performance, especially with the complexity of Michigan weather.
After much research we are confident in a retro-fit gutter guard that installs on existing gutters. The product is 100% aluminum, and we have observed over the years that this particular type does not allow biological material or roof shingle pellets through to the gutter below. The gutter guards we install are only about 50% of the cost of fancy gutter protection, and they perform equally well.
With any gutter guard there is no guarantee that debris will not accumulate on top of your roof or the gutter guard itself. However, once a gutter guard is installed it is very easy to sweep off debris from the ground with a push broom installed upside down on a painters pole or broom stick. We put a 10 year guarantee on the product and labor of our gutter guard systems, if anything falls below the gutter guard into the gutter, or if the material fails withing 10 years we will come out and fix it at no extra cost.