Balisongs don't "lock" in the same sense normal folders do. Most latch open/closed. Basically it transforms into a fixed blade knife. The handles act as springs, which keeps latch in the latched position. So in this respect, the "strength" of the locking is the amount of pressure you need to squeeze the handles to disengage the lock.
But the latch itself isn't really relevant. All it does is keep the handles together. The "strength" of a balisong is maintained by pressure on the handles. The "lock" is really your hands. So long as you hold on to both handles, the knife will be effectively as ridged as a fixed blade. The only way it can "fail" is if you let go of one of the handles (or the knife itself breaks). Being able to latch a balisong open is more a convenience than anything to do with structural integrity. For quick cutting tasks, I don't bother latching it open. If I'm doing something that takes a while or requires some muscle, I'll latch it, but that's just so I don't have to hold it closed all the time.
Thus, the "Lock Rating" would I suppose be that of whomever's hand is holding the balisong, or the strenth of materials that the knife is made from.
For keeping a balisong closed, the latch is there for obvious safety reasons. Some balisongs are latchless (for simplicity, silence, and shorter handles), but these are usually carried in a sheath to prevent accidental opening.
So on the Spyderfly, it latches closed so it doesn't open in your pocket (it does have a pocket clip after all). But it doesn't really need to latch open. The shape of the handles add to the ease of keeping it open though.
This is why I like the balisong so much (other than the "cool factor"). It gives you the utility of a fixed blade with the dynamics of a folder. It's just too bad the sheeple can't realize these are benifits for safety, and not so we can kill people easier with a flashy knife.
