In 1926, for an exhibition of some sort, Mart Stam, a famous designer in Europe, designed a chair with two legs. "Wha!?" you say, "A chair with two legs?" Yes. It is a design that you have undoubtedly seen, perhaps at your slightly too modern dentist's waiting room. It is the cantilever chair. I imagine slack jawed gawkers staring at the chair and then waving their hands were the back legs should be. The idea of the chair is that the use of new materials, in this case tubular steel with a high tensile strength, coupled with impeccable design could balance or suspend a person's weight on a cantilevered seat. The design, aside from being striking, is a perfect example of innovative design in an object that is so old that innovation seems impossible. We have had chairs with three or four legs for tens of thousands of years and then Mart Stam busts out the two legged chair.
What does this have to do with the Spyder Hole? Well, two things really. First it is an example of less being more through good design. Second, it is, like the cantilevered chair, and example of innovation in a space so old that innovation seemed impossible.
I am sure that someone down through the ages had thought of the hole opener before Sal Glesser did, but no one, and there can be no real dispute about this, has promoted it as well. Here is the thing about Glesser's innovation, and the reason why I think he should be viewed as not just a great knife maker, but a great designer (not "knife designer" though he is clearly that, but just "designer"), it is something that ADD features by REMOVING something. The hole makes knives easier to open and it reduces weight without reducing strength in any meaningful way. It also, in many cases, adds to the grip of the knife, giving your thumb a place to rest in high pressure cuts and preventing your hand from sliding forward in stabs.
Compared to the inelegant thumbstud, the hole is genius. You don't need additional parts. You don't need to figure out a way to attach the stud to the blade. You don't need to spend time and manpower attaching the stud. Just drill a hole and your done. Its simplicity of design carries over into a simplicity of manufacturing. Additionally, unlike the thumbstud or thumbplate, is does not attract gunk and pocket lint (though you can get finerprint swirls on the blade around the hole). It is simply a better solution to the problem on one handed opening.
The flipper, especially a well executed one, like on Gerry McGinnis's knives, is a thing of beauty as well. Perhaps not as pocket or retrieval friendly as the Spyder hole, the flipper does double duty as well, acting as a finger guard. It is more difficult to make than the hole, but it is a pretty elegant solution in its own right. Still, the less makes more of the hole, in my mind gives it an edge in terms of design chops.
In the end, the Spyder hole and its dozens of imitations, solved a problem with folding knives and made the need for automatic knife much less acute. And it did it with a design flair not seen since 1925 and the two-legged chair.