The New designz bolt is the only one with an oversized and angled inlet port. I found that the efficiency and slight fps increase was well worth it, especially when you combine it with the RIP valve, which is available from NDZ again.
If you don't have the RIP valve, you have no idea how much of a leap in performance it gives. I got about a 20 psi decrease on HPA if I remember right.
No more "Ding" sound from a valve spring during firing.
Huge efficiency/FPS gain
The spring is internal, so less parts to keep track of.