The test that decides it
Stand back from the house and look at what is above the roofline. Branches over the roof mean debris reaches the gutter in real quantity, and guards save real clearing over time. Open sky above the roof means very little reaches the gutter in the first place, and guards have little to save.
When guards are worth fitting
Guards also earn their place on a run that is hard or costly to reach. Cutting down how often anyone needs to get up to it has value beyond the clearing itself.
- Properties where nobody is keeping up with clearing on their own
When guards are not worth it
Guards are not worth it on a gutter with an existing problem. A run that is undersized for its roof, or has lost its fall, overflows no matter what sits over the top of it. Guards on a faulty run are money spent on the wrong problem, and it is worth ruling that out first.
What guards do not do
Guards keep out the bulk of leaf and twig debris. Finer material still gets through and builds up over time, so a guarded gutter still needs checking now and then.