Thanks for the comments, and for continuing the discussion. ***Craig - Great drawing regarding the use of pliers, which really does an excellent job of explaining the differences.
To further everything, I agree with selecting the right tool for the job, though debarbed every hook with my Renzetti for over ten years (and other vises for ten years prior) with no incident to the vise. Additionally, I can only think of a handful of hooks that broke, though I believe nearly all were due to imperfections in the hooks themselves. I am not a commercial tyer, thus would not be comfortable personally making a recommendation for an individual tying in bulk (though others have). As the video continues, vises with the jaw mechanism similar to a Stonfo Kaimen or Regal are absolutely not recommended for this purpose.
From personal experiences, I have had to sharpen more hooks after debarbing them with the pliers "end on," though definitely acknowledge the engineering perspective that Craig so expertly diagrammed. When taking the additional sharpening into consideration, the obvious answer is barbless hooks. We are fortunately in a time when the selection of barbless hooks has been constantly improving, with the cost decreasing, as Craig pointed out.
Many fly fisherman still prefer a barb, hence one of my purposes of this video is to educate and gently prod those to debarb and hopefully purchase barbless in the future.
Thanks again for the comments to continue this topic, and I hope you enjoyed my story regarding my Uncle John's Light Cahill during the video!
I'm with Colin. Vice jaws are not made for de barbing hooks, use the correct tool for the job.
The best solution will always be to buy barbless hooks in the first place. In the manufacturing process the hook is formed before the final coating (bronzing etc.) is applied. When you de barb you will inevitably break this coating, making your hook more prone to rusting. A barbless hook will always be preferable to a de barbed one. Barbless are more available in a wider range of shapes and styles than ever before. Until recently you could have been excused for thinking if you fish barbless you must fish dry fly. The only barbless hooks were all light wire. Not so today. Also buying barbless saves you a job.
Some people de barb while the hook is in the vice. This is prone to breaking the hook point off as, for all intents and purposes, the hook is held solidly in a fixed position. Hooks, as Tim observes, are better today, but the process of forming a barb hasn't changed in the last hundred years. Automation has only automated the process, doing by machine what was done with hand tools before. A blade cuts into the wire turning up the top part of the wire to form the barb. At the root of this cut you will get very small fractures in the metal. That is why hooks will still break while being de barbed. Lots of people have observed that if the pliers are used end on, rather than across the barb, the hook doesn't break. A friend of mine recently posted this elsewhere. He said that he didn't know why it works only that it does. (Being an engineer the answer is so obvious I couldn't believe he didn't see it). I did him this sketch to explain why hooks break, and why turning the pliers 90 degrees stops it.
Smooth jawed pliers, as Tim uses, can be difficult to find. If you are struggling look for jewellers tools or lapidary supplies.