I have shot both string loop and off the string ,so here is my take on it .I prefer to shoot a string loop apposed to shooting off the string .I agree it does damage the serving ,but if your in the habit of replacing your string every year,as I do .Shooting off the string isn't too much of a concern unless you shoot alot .I've never tried the loop your speaking of ,but I don't think I'd care for it because it add's weight to your string slowing down your max FPS ,but if it doesn't bother you to lose a few FPS then maybe it'll be fine . You can also learn to reserve your string which can also be a plus if your shooting off the string .
But either way you need to decide which way you feel most comfortable shooting ,off the string or the loop .

nubo