Gutter guards are worth it for houses under trees, and less so for houses in open lots. If your gutters only collect a little roof grit, a yearly cleaning is cheaper than a guard system.
The type of tree matters most. Large-hole screens handle broad leaves but let pine needles through. Fine micro-mesh stops needles and seeds but needs the occasional rinse to clear pollen. Solid covers shed debris well but can overshoot water in very heavy rain on steep roofs.
Guards also only work over gutters that are in good shape. If the pitch is wrong or the seams leak, a guard won't fix that, so the gutters should be cleaned and checked first.
No guard is truly zero-maintenance. But the right one can turn several cleanings a year into an occasional check, which is the real payoff.