I have a few houses to deal with....and LOTS of trees....big oaks, pin (willow) oaks, maples' whirly birds, etc.
I've used the short 4' flat aluminum ones that cover the gutter....screwed into the wood and also into the top front of the gutter...on shorter runs at several houses. Also had the same installed over new larger gutters at parents' house a few years back....pros did those....the gutters were continous (90'), but the leaf guards were 10' sections. Not perfect, but after a decade or so...I'd do the same thing again...just sooner
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