I have seen 3 of the Ultra noks after they broke and made an ugly mess when the guys were at full draw. I have also seen strings break right where the UltraNok hooks on but I have seen the string break where the brass nock set it clamped if it is clamped too tight. Go with the String Loop. A man in Kansas had his eye hit with a UltraNok, luckily he is not blind but did injure his eye. String Loops might break but they won't blind you.