Posted this on the excalibur forum too and bj who has his own archery shop and is a nice guy to deal with had this to say

i've use these for years...they're great...the more tattered and battered they get, the better they work...it'll change the twang into a thud and minimized the vibration ...i also use them on my trad and compound bows...

Wayne........

I'm wanting to use these on a compound crossbow and do not have a bow press so it will be a while before I can try them out.
Is there a way to split a string without the a press, it is not twisted.
Thanks Martin