I think the flap (pony express) style would leak water when driving in the rain, whereas the box type lid does not leak (at least in my experience so far). That is why I bought the box lid type. Just my opinion though.

--Tom 02 TBA; 130 mains; TBS; Nology Coils&Wires;Unifilter/opened Airbox; -AI/snorkels; -2 baffles;Progressive 440s & Springs