WOT warned me against that Stivi.
I did get in there though to take a look. The fact is, that there is nothing inside that site actually speaking about Riot, and Riot hasn't said a single thing about it... If it was valid, it would be on your launcher, like everything else that Riot hosts and does.
Plus this is in the terms: RIOTPROMOTIONS IS A WEBSITE ("RIOTPROMOTIONS,", "WE," "US," OR "OUR"). THIS IS A LEGAL AGREEMENT BETWEEN YOU ("YOU") AND RIOTPROMOTIONS. WE ARE NOT RELATED TO RIOT GAME IN ANY WAY