I haven't used them, but there have been a few short articles in the Travel section of the Sunday Boston Globe, about people using them and having them cut off. It seems that not all of the screeners are aware that there is a master key, so they don't need to destroy them.
I have been using tie-wraps lately, and if they cut them off, who cares? Just remember to put some extras in your luggage for the trip home. Oh........... and make sure you have something to cut them off when you get to your destination (I put small nailclippers in an outside pocket of my checked luggage).