Hi,
The screen in the outlet everyone should use even if leaves are not a problem. All it takes is one tennis ball and you could ruin your house.
If you do not mind cleaning your own gutter or your leaf problem is not severe use the sreens in the outlet.
The screens will keep your downspouts from getting clogged. If your downspouts get clogged you have to disassemble them to clean them. With the sreens in the outlet the water will still drain slowly. Most of the leaves after they dry out will blow out.