I just recently bought mine, as I used to work for the Renault dealer I asked how easy it was to put on, and the honest answer I got was I wouldnt try do it yourself as it involves drilling into the original spoiler then having adhesive applied.
I got one of the bodyshop guys to fit it 'out of hours' took him a couple of hours and it cost me £40.
I was also told to avoid getting it wet as the adhesive takes 3-4 hours to set.
Word of advice: the silver screws what come with the spoiler direct from Renault need to be replaced by black ones as the silver ones stick out like sore thumbs, shame they just dont send the right colour.