Had them on some VOLVOs (like 1974 & 1994) - they were great, would only come on if the parking/side lights were on, cut out if you put the headlights on. 2008 Ford Focus were hopeless. And it hasn't been foggy since I got my PRIUS.
I got mine installed but it's tied to the parking lights as well as low beams (didn't do anything special. It's how the car was wired. Weird). It gives a unique signature with the DRLs, front parking light and the fogs on. The front-facing parking lights are now back to incandescent so they match the colour of the DRLs and foglights now. They were previously LEDs to match the HIDs. The Gen 2s were more like driving lights so that other people can see you. In addition, the lens were really hot (steaming after driving in the rain) and eventually will crack.
The awful thing about 'style' fogs these days is they have widely spread beams, which when used as DRLs can dazzle other drivers. The old fashioned one had a flat fan shaped beam with a sharp cut off (like dipped heads do, but with no kick up) which mainly illuminated the kerbs to the sidewalks, etc. The would not dazzle other drivers. .. enough, already! I'll get off my latest soapbox and find a darkened room somewhere.
I remember the confusion as to how they should be wired, when rear fog lights became a compulsory fitment in the UK, early 80s IIRC. I drove a truck that had just been retrofitted with rear fogs that were wired up to the dipped beams and went off when you put main beams on, very confusing (and annoying) for the following traffic.