The main obstacle in fitting the fogs is routing the wiring through the bulkhead to the relay and switch:
If you are happy to drill extra holes through the firewall, then great - go for it.
Personally, I am not happy with doing this and I only ever route through the existing wiring conduits (ask A2OC member PC759 - when I did his dash swap, I left a draw wire in place whilst the dash was out, so that it would make the routing of wires easier in the future if needed).
The basic wiring and fixing of the lamps is straight-forward enough, but the fogs themselves are pretty much useless in fog!
Coming back from Whitby today over the moors, visibility was down to about 20-30 metres in places and the fogs helped not a jot in terms of me seeing out to the road! The oncoming traffic will not see you any better than if you have your dipped beam on either, so as Murdo says, save your cash and get a decent HID upgrade instead.
Cheers,
Mike