I expect that the efficiency and efficacy of the various gutter / leaf guards depends upon where you are and hat kind of tree debris you get.
I'm in Portland, OR. We get big leaf maple leaves, alder leaves, some oak leaves, but more d@*N Douglas fir needles than you'd believe.
Over 30 years in this house I've used at least four different gutter guard type products, all of which were utter failures with the Doug fir needles, which filled the gutters in no more than 60 days. I could have been cleaning the gutters 6 times a year if I was that ambitious, and I wasn't. Three times a year was more than enough for me.
Last year (Spring 2006) I found something that worked. No, I don't manufacture the stuff; I don't distribute it, I don't retail it, and other than on my own house, I don't install it.
I did test it for about 16 months by installing it on the back of the garage, to see how it worked. It worked very well. Its not absolutely perfect. Some stuff still gets into the gutters, but I believe its less than 5% of what used to accumulate. I've only had to clean that gutter once in the 16 months, and it was no where near full. It used to fill up to the top of the gutter with the Doug fir stuff, and made a great growing medium for dandelions and other cute stuff.
Its a white 3 foot long PVC product about 6 inches wide with a cross hatched PVC base with 3/8 - 1/2 holes in the base. Over it, and heres the key for the fir needles, is a white PVC screen that has maybe 1/8" holes. Water drops through, and drains through the gutter. The crud collects on top of the screen, dries, and the wind blows most of it off.
It installs by sliding one flat end under the lowest shingle row and snapping a flange kind of thing over the front lip of the gutter.
The first batch I bought were at a local Lowes for $ 1.97 a three foot section. First batch had a label on it identifying it as a "Snap In Gutter Filter", made by a company called "Gutter World", no web site or street / city/ address on it. I used white, but they had them in brown, too. "Made in U.S.A." on the label. The product UPC on the first batch was: 0 17857 00461 7. No patent number on the label or the product.
After last weekend's check of the test batch at the back of the garage decided to do the garage front and the front of the house. Went back to Lowe's, they still had the things. but with a slightly different label, but still identical art work, indicating the manufacturer to be Amerimax Home Products, Inc.; still no website listed, still no city, street address or state. Still "Made in the U.S.A." Does have a different product UPC, now being 0 49821 86270 1. Still called "Snap In Gutter Filter". Again, no patent number on the label or the product. I got the white again; they still had the brown, too.
And best of all, the 3 foot strip is now $ 1.47. Less than $ 15.00 bucks for the garage front is a real good number in my book. The 60' front of the house, which is tomorrow's project after I empty the damn gutter this afternoon, will run less than $ 45.00.
I noticed no deterioration in the PVC on the test batch. Apparently no ultraviolet effect in the 16 months those have been up. Then again, this is the west side of the Cascades, so we only get sun on July 17, except when its raining, as it was this year. (G)
I did the install on the 30' foot width of the front of the garage in about 10 minutes this morning. It took a lot longer than that to clean the damn gutter.
Just my $ 0.02. YMMV. No guarantees. Might be worth trying a test strip on one gutter if you are plagued with fir or pine needles.