You will not get banned for using Blitz, since it doesn't give you any advantages in the game. Blitz just takes publicly available data and contextualizes that data for you in real-time while you play. You still have to play like everyone else.
In fact, people from Riot Games and Tencent are using Blitz too! We talk with Tencent and Riot before developing any major features and make sure they are okay with what we are doing! Read more here.