I have an old late 80's USA Soloist that has that lock behind the nut. It works perfectly. In fact, its the most stable (trem) guitar that I own. The actual lock nuts have a slot rather than the hex nut, so you can use a coin if you have to. I can dive until the strings are completely slack and hold it there for a long time with zero loss of tuning.
It doesn't seem like it should work but it does.
Hell, the guitar sat dormant, in its case, from about 1995 through 2008 and was in tune when I opened it up. Nasty, but in tune!
On the left...after all these years I got it refurbished and its one of my favorite guitars.