Hello FTers,
I think that all bags are X-rayed, so there's no reason for the TSA (here or in Europe) to search through the bags without us presence.
What I use for locks are those cable ties. I keep a bag of them in front pocket of my checked bag along with a pair of scissors. It's inexpensive and you will know if someone had broken into your bag.
I have the TSA-approved locks, but haven't used them yet.
David