Thats one of the better mods to a prefacelift bumper fella, it got me thinking, have you tried covering/painting the thin red strip just below the foglights? I think it would bring on a slightly more s4-esque appearance and break up all that red.
If I was doing that I'd get the Cupra Championship spoiler, not that 80s whale-tail job! It would be hard to do properly though, without it turning into a chav-mobile.
Another pic then...
As for fitting, this pic actually helps explain this in a way - I trimmed the centre posts down but not very evenly at first (tricky to judge) which is why it seems to bulge down on one side a bit. I've sorted it since that pic was taken so it is actually straight now! I was reluctant to cut the bumper, the splitter is only £20 so I'd rather cut that down than a £300 bumper! Its held on with some self-tapping screws from B&Q, I think four on each side. Getting it central is the hardest part, rope someone else in to help you! Also the ends will poke into your wheel arches but don't cut them until its on the car so you can get the length right.