You won't get banned for using one unless your a douche and use it on almost every game. People will start to notice and they will report you, and if you get enough people to negatively report you, you will get banned. Otherwise there is no way for Microsoft or the makers of the game to provide solid evidence that you are not just on a bad connection and are indeed "cheating". I have used one for quite a while now and I have had no trouble. I do not use it very often though, only when I am provoked or when the other team is somehow cheating or just being really cheap.