Check with manufactorer and installers on warranty.
" They (inserts) look to work pretty well" Well no they don't. I've tried all sorts. But then no guards work really well. They all work, ...well...sorta. Even those one piece leaf excluding ones work sorta. And they can't handle a Texas gully washer, no matter what they say. The leaf ejecting ones don't eject it all. Any thing you put over or in your gutter is going to be a place where leaves, snow and ice can accumulate, as it can in an empty uncovered gutter. Leaves don't all blow off or out,when they get wet they pack down creating places for more leaves,snow ice.The gutter itself can be completly clean but ice,snow, leaves on top prevent water from passing thru.You get leaf dams and ice dams. Snow and ice can build up in gutter and overflow thru screen and pile up. Debri and ice can build up on steeply slanted screens. The best add ons I've found are steeply slanted fairly open grid with higher ridges running across the gutter, even then leaves can get between the ridges, stems stuck in grid. I can't find them any more anywhere. Ice is not a problem here usually, at least not lasting long enuff to be gutter and roof wise, If that is a major concern of yours I would stay away from any flat topped guard, or brush type insert.
Measure twice, cut once.
Look at the nail, not the hammer. Watch the fence, not the blade.
If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.