Why?
And by that, I mean that I fail to see any point to a lock on a handgun. I know they are currently all the rage with the safety nazis and bliss ninnys, and that many gun makers have included locks into new designs, in order to be able to sell their product in various jurisdictions.
But I have to ask WHY? What earthly good can a lock do, other than to put you at risk? An unloaded gun is nothing more than an oddly shaped lump of metal (and nowadays plastic), and useless as anything other than an impact weapon.
A loaded gun should not, must not have a lock on it. Any kind of trigger lock on a loaded gun is idiocy! The only thing that belongs on or around the trigger of a loaded gun is your finger, and then, only when your sights are on your target!
I fail to see any point to a lock (non trigger) either. Mechanical devices, locks included, can, and do fail. Leaving a loaded gun unattended, trusting to a lock is foolishness. Sure, as long as the lock works, you would be "fine". but if a lock should fail, you are still responsible. And in a defensive gun, there have been documented cases of locks failing, in the locked position. Not a risk I would voluntarily acccept in a tool that I might have to use to save my life or others (no matter how statistically slight). I believe that the time needed to unlock a loaded gun (assuming you accept the argument that you should do so) would be better spent loading an empty gun instead.
If you need secure a loaded gun (and again, I have to ask why?) you lock the gun in something (like a safe). You do not lock the gun, leaving it out, and available to unauthorised hands.
Put a lock on you unloaded gun if it makes you feel safer. Its your gun, do as you want. But be aware that thats all you gain, from a safety standpoint, a good feeling.
Securing a gun against theft is a different issue. But even there, I go with locking the gun in something, not locking the gun with something.