Bug deflectors?
 

you know, those little plastic bonnet mounted windshields that divert the air, so the bugs go over the roof not on the screen, do they help any in day to day aero stuff?

No.

full separation
 

I have an old VHS of Texas Tech University's 'Project Headwind' in which they video-graphed smoke flow over a model F-250 Dualie pickup with various aero mods.
An upright bug-deflector caused complete flow separation over the entire bonnet,windscreen,and header.
Textbook terrible!:eek:

Yet they sold a ton of them, and still do in some parts.

The ones they have today on cars lay more flat and contoured to the hood...of course the bug deflection factor minimal and it is also integrated into a hood edge protector from debris and such.

The old flat ones make a good lower grill block on a 2008 smart with a little trimming. Chumly

Ah so they can improve fuel economy, if used properly.