Well ay bigger front (i take it you mean bumper) will still not open access to that area.
The area where these vents fit, is right at the top. If I remember correctly, the metal reinforcement plate also has to be cut behind the bumper cover so that they sit far enough, and direct air to the intercooler.
IMO it probably is effective, but again IMHO very slight, and probably not a noticeable gain at all.