It annoys me no end that so many of todays auxiliary lights are just bling
I agree, though I'm even more annoyed by the mountain of aftermarket replacement main headlamps that are just bling.
I find myself thinking that the Cibie 175 was arguably (some would argue for the Marchal 950) the best foglight in the world in the 1970s
It's difficult to pick a single winner; there were a lot of very good halogen fog lamps in the 1960s-'80s, and many of them were from Cibie or Marchal. The performance characteristics of the various models were different -- the Marchal 700 produced an almost impossibly wide beam, but it was not very deep. The OscarPlus produced a narrower but deeper beam. All of them had a relatively large amount of flux within the beam. The trouble with them is their size and bulk; they were well adapted to yesterday's big stamped-sheetmetal bumpers and valence panels. Today's front ends aren't really configured to host a set of big, heavy lamps. Even an adaptive mounting setup like
the Carr Light Wing is suitable only for those vehicles with solid metal bumper structures readily accessible at the front license plate mount point. Nevertheless, some of these really good big French halogen fog lamps remain available.
It's a lot more difficult to make a good small fog lamp than it is to make a good big fog lamp. It's not impossible, but it takes a lot more thought, care, effort, and
money. There are some very fine fog lamps (as fog lamps go) in the pipeline; the ECE and SAE standards have been updated recently to provide a new category of fog lamp, "F3", with better performance requirements than the (very) old previous specifications. The new F3 fog lamp has recently or will soon become mandatory under ECE regs (fog lamps themselves will not be mandatory, but if they are installed they either must or will soon have to be of the F3 type). One such lamp that comes to mind is Osram's JFL2 Joule LED fog lamp, which is
very small but quite good.
The reason for the "as fog lamps go" disclaimer is that even good fog lamps are of little use to most drivers. They're for use in severely bad weather to help the driver see the edges of the road close to the car so he can grope his way along at very low speeds. Fog lamps do not meaningfully improve seeing or safety in other-than-very-foul-weather conditions, though many drivers misuse them in the mistaken belief that they can see better at normal road speeds in dry weather. See
this thread and look at the data in post #4.
(And while I'm at it, how come auxiliary low beams, like the Cibie Booster Beam and the Hella XL have gone the way of the Dodo?)
They were never very popular. They're not Federally regulated, never have been, and the SAE standard that specified the design, construction, and performance of auxiliary low beams, J582, has been cancelled and withdrawn. The concept was attractive to drivers stuck with not-very-good headlamps, but iffy under the terms of many state vehicle codes' lighting requirements. And in many (most?) cases, they were just another pair of improperly-installed, improperly-aimed, improperly-used lights on the front of the car (bling again).
So what's the best add-on fog lamp? Probably a carefully-chosen low beam with a sharp cutoff, a broad beam, strict control of upward stray light, high peak intensity, and a low aim angle. I have had good results with the Hella Bifocal or (discontinued) Cibie complex reflector 5¾" H1 low beam and with certain varieties of the Hella 90mm low beam module in "fog lamp" service. There is a case to be made for selective yellow light color.