I never really paid attention to the zippers much in the past, I guess I thought they were a bit too busy looking. Then Norb let me shoot one of his extreme's at last year's Texas Sweat and everything changed. Three basic reasons:
1. I find that they are the most pointable bow I have ever shot. I am consistently more accurate with a zipper, right out of the box. Norb's was that way, Christopher's, and now Joe's that I am trying out. In the words of Charlie Lamb, "If something happens twice, it may be a coincidence...if it happens three times its a pattern"
2. They are unbelievably quiet & fast. Quiet as a longbow really. The zipper extreme that I tested clocked in with a range of 168fps with cedar shafts up to 196fps with 600grain carbon shafts. My Brack Quest came in consistently ~ 10fps slower with the same arrows. I want to do some more research this weekend, but I am impressed.
3. Pictures don't do them justice. They are very nice to look at with lots of subtle detail, and they fit your hand like a glove.
I think you will find the same results.