The only ones I've heard of (and thought I'd seen) are basically weak headlights that don't help but are supposed to (do I notice the lights first, in the middle of the day, or the giant car? it's the giant car, of course), and just look bad. IMHO, obviously. ;-) I'm just not fan of the type I've heard of/seen.
Up here in Canada, every car has them - unless it's visiting from the USA. And they do work. It probably doesn't matter that much at high noon on a bright "severe clear" sunny day, but trust me, there's lots of days where the visibility isn't 100% and many people still don't bother turning on their headlights.