Are TSA-approved locks actually secure?

Not very, and reviewers across r/onebag and r/lockpicking are explicit about it. Because every TSA-approved lock can be opened with a small set of master keys, and because soft-sided luggage zippers can be opened with a ballpoint pen, these locks are best understood as a deterrent against opportunistic pilfering rather than real anti-theft hardware. For checked airline bags they are still the right choice, since non-TSA locks will simply be cut off during inspection.