used the metal loop for several years when they first came out.never had any problems other than the release pushing the nock loose from the string. replaced them with shorter nocks and never had any other problems. as for it slowing the arrow down because of the string weight it never seemed to effect any of the deer i killed, even out to 40 yds.been using a string loop since 2001. like it better because i can adjust it to length when tying it. just make sure you check the knot frequently and look for frayed string. other than that there was no noticable difference but i am sure some one will have to disagree me.