I have the factory git factory installed when I bought the car. They work like any other fog lights I have had. To me fogs are to light the road from a low angle and really only provide a good clarity for what is close to the car (meaning maybe 20-30 feet or so).
I had the factory fogs on my 08 Spec.B and the bulbs never had to be changed in the 3 years I owned it and they lit the road just as good as my 2011's do.
Personally I'd go Subaru OEM for ease of installation and warranty.
I'm just here for the mods.