I'm the dude that has one fitted and I can tell you they are well over priced £1000 for upper and lower parts of the spoiler(i stupidly paid it though ha ha) the upper wing I got needed some serious work from the bodyshop shop to get it near perfect and smooth ready for painting once we got passed that it's real easy to fit take the current spoiler off install the lower spoiler then bolt the plastic bit that holds the lower spoiler in place then fit the upper wing over the top drill two holes through the tail gate then line it all up then bolt it down.
That's what the bodyshop told me how it was done 30 mins fitting time.
It does transform the car considerably and I'm very happy with it .