Hey Murph, I use them on some, but not all, of my knives. They are especially useful on some of my fishing knives "spyderco salts" that I carry in my waistband. They help me access the knife wile in a seated position (kayak) and also make it easier to hold onto. I also tie these with enough loop to slip over my wrist, which I do when I'm on the water and have a big fish flopping around. They can be fun and useful depending on how you use your knife.
But don't buy one!! Half the fun is getting some paracord and tying them yourself. Search youtube and find a good simple how to video (there's hundreds) and just follow along. I have zero patience for such stuff and even I have made some really cool ones and there was nothing to it. Get yourself a couple of colors of paracord and give it a shot! You will enjoy the results much more that way.
Suerte,
Lance