FlapGuard Combined Brush + Flap

This is the most thorough option on the list — it pairs a brush seal with a secondary flap that closes behind it, so you're getting two layers of draught protection rather than relying on bristles alone. It also noticeably cuts down on the rattling noise a loose metal letterbox flap makes on windy days, which isn't something the brush-only options address. It sits a bit bulkier on the inside of the door, so check clearance if you have anything mounted close by, like a coat hook or shelf.