Forget about TSA, checked luggage is handled by all kinds of people from the point where it is checked to the point where you pull it off a belt at your final destination.

Locking a bag only flags it as containing valuables, it doesn't stop the lock from being cut or the bag from being sliced open.

Every COC I've ever seen relating to baggage expressly disclaims liability for valuables in checked luggage. So, put them in your carry-on or ship them via an express carrier and insure appropriately.

TSA does both random and specific searches, so as a statistical matter, if you travel enough, your bag will be opened. I've never had a problem, found anything particularly medded and and never had anything go missing. But, then again, I rarely check luggage and, when I do, most certainly don't check items of value.