Re: Need help choosing an S Series.
I own a Prestige RG2560 with an Edge Zero, and as a backup for gigging, an S570. Both guitars are professionally setup, with the ZPS removed from each. In my opinion, the ZR trem is superior. Stability is much better, returning to zero point very well even without the ZPS. Overall feel is a touch lighter which I personally prefer. The arm collar is much better, I know many people haven't had trouble with this but the pop-in system of the Zero was a nightmare for me as the spring was too tight, causing friction even with lubricant. I had to replace it with a Schaller collar system. And above all, the ball bearing system, as has been noted already, will never wear. From an engineering perspective it's more competent than knife edges.
Also, flutter is very possible with both, if anything a little easier with the ZR. I've never understood this criticism, unless people haven't removed the ZPS, which would restrict both systems.