We haven't used the app, so we don't know how well it works. It might block legitimate tells from friends. If you try it out, tell us how that works for you.
The post at the Herald says that the mod is not endorsed by Mythic, although one would think that mentioning it on the official site is at least a tacit endorsement. Mythic did go on to say that players should continue using the game's built-in spam reporting features as well.