I tried making one of those last summer. However, I could not get it tight on the string, it would spin on the string and therefore it would move up and down a little bit.
I use a Catfish Loop, and use tied string nocks to hold it in place. If you take the time to serve it real tight, you can keep it from moving or spinning without the string nocks. You can use one string nock or two, place them outside or inside the loop or make one nock larger or longer. The nocks can be twisted up or down the string to allow for micr-adjustment of your nocking point.
There are many advantages to the catfish loop. It will not stretch even a little bit. You can easily custom make the diameter and length to meet your exact preference and duplicate it identically each time. It will not slip or come off, and I doubt one would ever break. I put 40,000 shots on one (slipped it on a new string when I replaced the string). It never did break. I just left it on when I sold the bow.