Garmin Lock is a power-on password. You can specify a location, for example your driveway, where the GPS will bypass the password. This is good if you forget the password or you don't want to take the time to type it in. You can turn the password off if you want.
My Nuvi 765 is supposed to have "Garmin Lock" on it, but I've never needed it... From my understanding though, it's supposed to work so as long as I'm connecting the GPS to the mount in my vehicle near where it was last disconnected, I'd notice nothing, but if somebody stole my GPS and tried to access the address data stored in device, as long as they don't have a compatible vehicle mount near where it was taken, the thief would need my password to gain access to any saved addresses I had stored on the GPS. If I have to reactivate the device and forget the password, as long as I remember the location of my "SAFE ZONE" and wait to power on the device near that area, I can reactivate the device and/or reset my password... But if I have a "Garmin Lock" password set I don't remember and moved to a new location, I'd then have to return the device to Garmin and have THEM reset the device password so I could again use the device.
They removed it because people used to forget their passwords making them unusable. I think this is really stupid on Garmin's part. You do not remove essential security features because people are forgetful. In any case, if you do purchase this unit, since it has no lock, make sure not to set the HOME location. Otherwise thieves could just steal your GPS, set it to GO HOME and go ransack your house while they know you are away.
Garmin lock is a feature that locks the gps. You can unlock by a PIN you select; or you are near your address you set for "Home". Useful if your gps is stolen from anywhere not near home. If tbey stole your car with the gps, and your door opener, guess what happens next. Moral.... set "home" away from real home. I know, I didn't answer the question. I have the 1390 and older 255 and 660 and they all had the lock.