They shed studs like crazy. I lost around 10 from each tire last year, which compares badly to my Nokians, which never lost any. I talked to Schwalbe about a refund, and they made friendly noises but failed to deliver. They do sell tiny packages of expensive replacement studs, but I'll probably fill the holes with Nokian studs which cost less and are probably better.
They do perform better than Nokians. However, once they wear out, I'm going back to tried and true Nokians. I'll take quality over performance any day.
Paul