So, yes, you must use TSA locks going or coming or in the good old USA.

However, the TSA employees, who have the keys to the locks, are as guilty as baggage handlers of stealing stuff. Recently, a TSA agent in Florida stole over $50,000 worth of electronics from checked baggage in a 6 month period. He would stuff iPads, GPS receivers, you name it, down his pants. He would sell the stolen items online. Just go to news.google.com and search "tsa thefts". Plenty of articles to read.