When one can break into most zipping suitcases with a bic pen, rezipping it so you never know I was there, what's the point of a lock?
[0] http://www.amazon.com/Kolumbo-TSA-Lock-2-pack-BLACK/dp/B0106...
You just use something like a pen to break the zipper mesh. Sliding the zipper back and forth when you're done will re-zip it.