I'm with Leon. I ignored them, didn't like the ones I tried, etc. I figured it was just one more gimmick to sell to deer and elk hunters.
Mountain hunting for elk has changed my mind. Many people out here quarter and/or bone out their elk (and, if you're back a ways, deer) by splitting the skin down the back (where it is thick, and lies tight to the animal, making the two fingers trick almost useless), then making vertical cuts down the legs. You pretty much don't gut the animal except to get at the backstraps and organ meats. It's unbelievable how fast and cleanly you can do an animal this way. The meat cools faster, and all the mess and unnecessary weight gets left in the brush. Leon's right about small hooks binding, of course...that's why I just PM'ed him and why I'm also checking out that cheap Gerber tool.