I have no faith in foam or plastic. Maybe 5+ years ago I put the "Gutter Glove" product on about 20' of high gutter at our lake home. I did this specifically as a test and I am able to look at that section of gutter from our bedroom window. Bottom line was it worked well. This is a stainless screen on an extruded aluminum frame, so pretty rugged.
As a result of this successful experiment, I put the product on our city home last year, including some heated sections to eliminate ice dams. It is working well. I am happy. There is, however, about a 3' section that does get pine needles. The contractor sent someone out to clean that section, part of his guarantee, but he is an older guy and probably will not be around forever. The guy that did the cleaning said the needles were trapped in a seam, which sound to me like it could be closed up with silicone caulk. We'll see.
Gutterglove.com | Stainless Steel Gutter Protection These are installed by independent/franchise contractors. FWIW I found that most of the sellers of various magical gutter devices are willing to haggle on price. I ended up paying about 20% less than the first-quoted price. It was easy; the contractor called for a follow-up and I told him I was still thinking about it because of the expense but if he'd do it for 25% less, he could come over that afternoon. He countered at 20% and I took it.
The Gutter Glove product seems to me to provide the most value. Foam and plastic are both extremely cheap to manufacture and highly likely to deteriorate over a few years.