I'm personally not a fan of metal loops... I think they would add too much weight, might be prone to "clicking" when hooking up... and I know in the case of my Scott Wildcat, I wouldn't even be able to use it since the jaws are made of aluminum in anticipation of hooking up into a rope; the instructions say not to even use it with a brass nock because of premature wear.

Maybe in a couple weeks when things settled down here job-wise (I keep posting after I about go stir-crazy while working on this huge project to give myself a break) I can do an instructional thread on how I tie in my nock sets and string loops.