So much so that FIFA was looking into banning them from the games. All they really are is a cheap peice of plastic the makes a buzzing sound when blown through (properly) but a few of the players, and understandably TV viewers are complaining about the sound. Well it looks like the TV portion has been somewhat solved or atleast reduced. The players that have been complaining about it, are stating that they can't hear each other, and even exhaust themselves yelling at their team mates. I really don't see how different it could be from a typical EPL game. But then again I know for a fact that Football stadiums can get extremely loud. Like Arrowhead Stadium in Kansas City has been measured at 116 decibels, and I think that your ears start to bleed shortly after that. Apparently with all the horns going the sound can reach up to 144 decibels (the same as a passenger jet or equivalent,) and I know that you start to suffer signficant hearing loss after 150 decibels.
It seems like some players and coaches don't mind. One player was able to talk his way out of a yellow card (which is pretty difficult to do) because he said that he couldn't hear the ref blow the whistle. One coach welcomed fans to bring the horns to a public practice, because he wanted his players to get use to it. Sounds like somebody is trying to roll with the punches. I think it would be smart if teams started practicing nonverbal queues, which if done correctly can through off opposing teams, but that does take a lot of paying attention to your other team mates when your suppose to be paying attention to a ball (especially if you don't know where the ball is going to bounce off too.)