Add-ons have to be installed over an existing or new open gutter. Screens and filters are placed in or clipped or screwed on to your open gutters. Most of the larger hoods, covers, and helmets actually have to be attached to your roof gutter, with screws, nails or glue in order to work. Putting holes in your roof is a bad idea and it can void your roof warranty.
Also, add-on covers are often noticeable additions that can look bulky and destroy the finished look of your home. Whether the add-on fits into your existing gutter or perches on top of it, add-ons can fall into the gutter after heavy snow, or be blown off in high winds.
This cannot happen with a LeafGuard gutter. It’s one-piece design, heavy-duty construction, and durable non-corrosive hangers, keep it safely attached to your fascia board.