The last thing you want to add to your string is a metal loop, unless you are looking for more trouble than you can handle. Some might argue the point but it is absolutely one of the worst things you can do with a bow.
ive used them for over 10 years as well as my 2 brothers. not a single problem.they actually get smoother with age.it provides a way better solid feel when you lock up with the release. i tied a loop on for a couple weeks and then took it off. in archery its whatever works for an individual. ive seen a bunch of failed loops through the years but my ultra nock keeps working. its been on my current hunting bow since 2000 and it was on my bow before that.