Sadly, my present budget is sufficient for only the Vaquero Grande and the Sifu. And although I love both of them, they do have their inadequacies
OFFICIAL DISCLAIMER: My experience with these knives has been limited to my particular knives only. This posting does not pretend to present an opinion representative of all the other knives of these models.
I have found that thumb opening the VG is pretty much a fruitless effort and have limited myself to inertial openings. The blade has developed about a 1/32" vertical play which is plenty of rattle room.
I bought the Sifu out of sheer hope that the lock strength would allow the knife to be used for back cutting. I had one of those stupid moments and rather than taping the blade like I had intended, I took a very light back cut swing at my cutting dummy and now have a new scar just below the middle knuckle of my index finger.
I taped the blade and tried several more times and you couldn't stop it from folding. I contacted Mr. Taylor explained the situation, and sent him the knife. He and Mr. Brothers took it apart, checked it out and said everything was up to specs. They performed the spine whack test and said it worked fine.
I got the knife back, taped the blade, and it took several light back cuts without folding. Later on in practice, it began folding again. I took it to class and all of us took turns tapping the back of the point against our bare hands and watching the blade fold. It sat in the drawer for a few weeks and when I pulled it out and began tapping the point against my hand, it held.
I guess the lesson is that no matter how strong the lock may be, the spine whack test is not the same as back cutting. And at least in my Sifu, it can't be used for back cutting.
My large CRKT Krawford Casper folder with the intervening secondary lock engaged works fine for back cutting.
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All you need is love... a sharp blade and a full clip