From what I've read about the history of the navaja, the lock was actually something that was invented at a later time, but also served to make them more useful in an offensive or defensive situation. One could easily compare the sound of the carraca with the pump of a shotgun, except that large knives tend to scare the heck out of most people a lot more so than guns.
The truth of the matter is, for me at least, I'm not too concerned with the lock strength. I don't and probably never will, carry a knife with intent as a weapon. My first reaction would probably be to run like hell if I were faced with a situation that required the threat of murder, especially with a knife. I don't want to get into any kind of discussion about what is right or wrong, this is just what I would do.....
The historical significance is what interests me more than anything, along with a love for knives in general. I lean towards a 3.5" blade pocket knife and for that, the clasp lock is more than sufficient. Also, I am not one for spine whacking, so the truth is, I do not really know how strong these locks are. The extent of my testing is hand pressure to close the blade with the lock engaged and all have passed that test with flying colors.
If someone wants to purchase different navajas and do destruction tests, I would love to watch, but otherwise, I will continue to slice up my apples, along with lunch and dinner and be blissfully unaware if the lock can withstand a bloody fight to the death.